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~ Queen's University
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Volume II
Proceedings of the
10th CANADIAN ROCK MECHANICS SYMPOSIUM
KINGSTON, SEPTEMBER 2-4, 1975
Sponsored by: Department of Mining Engineering, Queen's University Canadian National Committee on Rock Mechanics, C.I.M. Canadian Rock Mechanics Group
Published by: Department of Mining Engineering Queen's University
© Copyright 1975, Queen's University, Kingston, Canada
Available by mail from Dept. of Mining Engineering, Goodwin Hall, Queen's University, Kingston K7L 3N6, Canada
Printed in Canada by Brown & Martin Ltd., Kingston, Ontario
TABLE OF CONTENTS
Ground Control in Transverse Cut and Fill Mining Operations at !NCO .... 1 P. H. Oliver
Application of High-Speed Photography to Rock Blasting at Canadian Industries Limited: A Review . . .... . . . . . . . . .. . .. .............. . . .. . 29
S. Chung, B. Mohanty, L.G. Desrochers and L.C. Lang
Slope Monitoring at Brenda Mines ...... ... . ..... . . . . ....... . ...... 45 G. Blackwell, D. Pow and M. Keast
Super Scale Resource Development .............. . .... .. .. . . . .. .. . 81 E.W. Brooker, D.W. Devenny and P.L. Hall
Monitoring of the Hogarth Pit Highwa/1, Steep Rock Mine, Atikokan, Ontario ................................. . .. .. . ... 103 C.O. Brawner, P.F. Stacey and R. Stark
Written Discussion .... . . . ... . ...... ... .. . ....... . . . . . .. . . . . .. .. 139
List of Delegates . . ...... . ....... . ........... .. .... . . . .. . . .. .... 143
List of Supporting Companies . .. . . . ... . ....... . .................. 158
Addenda: Corrections to Volume 1 ................................ 159
GROUND CONTROL IN TRANSVERSE CUT AND FILL MINING OPERATIONS AT INCO
P. II. Oliver1
Abstract
1
!nco has successfully utilized yield and span to control the effects of a high horizontal field stress condition on transverse cut and fill mining for forty years and yield to alleviate rockburst conditons for 35 years. The approaches used were developed empirically.
Ground conditions associated with deeper mining suggested the existence of high horizontal stresses wh ich were subsequently confirmed by measurements. A new t heory was requi red to ex pl ai n the effectiveness of the procedures . It was found that beam-column theory, as applied to a thin, tabular and ncar horizontal orebody to control high horizontal stress effec t s in room backs, was similari l y applicable to transve rse cut and fill mining. The theory demonstrates the validity of the techniques used by Inco in the Sud bury operations and suggests me ans to ef f ect fur ther improvements.
1s uper visor of Rock Mechan i cs , Mines Engineering, l nco Coppe r Cl iff, Ontario.
2 P. H. OLIVER
1. TNTRODUCTION
Ground control in transverse cut and fill min ing nt
Inca's Sudbury operation s, involves yielding pillars and
sequenced headings to alleviate rockburst condition s .
Yielding pillars in c onjunction 1~ith stoping spans, contro l
stress conditions in the immediate stope area. The yield
effect is influential in governing the mechanism of stress
reJief in crown pillars. The concepts of seque nce and
yield were developed over thirty years ago when the
principal stress was assumed t o be vertic al and the mining
method wa s overhand squar e set with crushed rock f i ll .
The two concepts have remained virtually unchanged
and are us valid today as they were thirty years ago, in
spite of the many changes in mining in the interim period
and the ever increasing depth of mining operations. Roof
bolts and screen have replaced square sets; hydraulic sand
fill, foll owed by cemented hydraulic sandfill has replaced
crushed rock as the fill medium; scooptrams have replaced
the slusher wh ic h had replaced the hand shovel.
Over t he past decade, it became increasingly apparent
that the accepted theories relevant to the success of
sequence and yield, could not adequately explain many of
t he observed conditions . There were strong indicat ions of
high hori~onta l stresses, but no means to explain the
observed r eduction in stresses in the stope backs associated
GROUND CONTROL AT INCO
with rib pillar yield.
The measurements of the stress state at depth by
Dr. Herget (1) in 1974 confirmed the existence of high
horizontal stresses, and emphasized the need to develop
new theories to explain why the yielding pillar mining
approach worked.
2. HISTORY
Fill method ground control began with the first lay
out of transverse stapes and rib pillars at Frood Mine in
the thirties. Stapes were 45ft. \vide and the rib pillars
35 ft. wide. The primary mining recovery factor was 64%.
Cut and fill mining was used and the fill material was
crushed rock.
The sequence consisted of dividing the orebody into
blocks, with each block having a strike length of from
400 to 500 ft. Barrier rib pillars, generally 66 ft. in
width, separated the blocks . Major floor pillars , SO ft.
thick, were left every second level to control level
subsidence (Figure l) . Mining on a leve l began with the
blocks on t he extreme ends of the orebody and new blocks
were progressively started, working inwards from the end
blocks.
It was soon found that artificial ground support was
required to control the backs of the stapes and mining was
3
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FIGURE I FROOO MINE BASIC LONGITUDINAL LAYOUT
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GROUND CONTROL AT IHCO
converted from cut and fill to square set and fill.
As additional stopes were opened, increasing the
length of the stoping blocks, heavy ground developed when
mining r eached approximately 40ft. from the level above.
It was found necessary to reduce the width of the stopes
5
and pil lars to 5 sets and 4 sets respectively, which
resulted jn stoping widths of 30.5 ft., including overbreak,
with the width of the remaining pillar being 19 rt.
The 5 set stoping width, in conjunction with 4 set
p illars, provided a primary recovery factor of 62%. 'rhe
fact that the pillars fractured was observed and it was
noted the Cracturing of the pillars resulted in improved
ground conditions in the stopes. The 5 set stoping
width provided optimum ground conditions from the sill to
the crown and was an efficient width for square set mining
with hand mucking. For the reasons outlined above, a span
which suited the mining method and a stope to pillar rela
tionship which optimized ground conditions, the 5 set stope
and 4 set pillar became the standard for transverse fill
method min ing. There was no theory involved in arriving
at this stope-pillar geometry, just the tried and true
system of observing what works and applying the knowledge
gainfully.
The sequence, mining from the limits of the ore in
t owa r ds the center, plus the major barrier rib and crown
6 P, H. OLI VER
pillar s, provided a fer tile field for rockbursts. The
increased incidence of rockbursts coincided with the severe
rockburst situation in the Kirkland Lake area and resulted
in the setting up of the Rockbur st Commi ttee by the Ontar io
Mining Association to investigate ways and means to predict
and control rockbursts and to co-ordinate the investigative
studies of the individual mining companies. The key
document r esulting fr om the efforts of the committee was
the report by Morrison (2), published in 1942 , outl ining
the doming theory and the importance of sequenc i ng towards
the coalesc ing and en largment of domes. the effect iveness
of the approach outlined by Morrison has been proven by
the marked reduction in the f r equency of rockbursts and
rockburst related injur ies beginning in 1941.
Inco has freely used Mor ris on's repor t as a r eference .
Stoping begins on a lead level and progresses outward from
the lead stope (Figure 2). No burrier pillars are left and
small rock inclusions are slotted through to avoid the
establishment of rockburst prone remnants.
The standard stope-pillar geometry, applied above the
4000 l evel horizon, required modification for mining t he
heavy massive sulphide ores at Creighton Mine below the
4000 ft. horizon. Stope widths were reduced to 3 sets for
a mined width of 19.5 ft., including overb reak , and pillar
widths were reduced to 3 sets fo r an effective 13.5 ft. width.
GROUND CONTROL AT !NCO 7
w (.) z w :::> 0 w (/)
(!) z z ~
0 0 :I: 1-w :E
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8 P. H. OLIVER
The primary extraction ratio was redu~ed from 62% for
the 5 set stope, 4 set pillar geometry to 59% for the 3 and
3 geometry.
In the early fifties , hydraulically placed classified
tailings 3nd alluvial sand replaced crushed rock as the
fill medium. Towards the end of the fifties, the increased
application of roofbolts began to spell the end of square
set stoping.
In the early sixties, the use of portland cement to
consolidate hydraulic fill came into universal app lica t ion
to improve ground conditions during pillar recovery
operations by curtailing fill l osses from mined areas and
by reducing f il l recompaction. The improvement of the fill
characteristics was achieved without increasing primary
mining method costs in that expenditures for cement were
offset by the savings in labour and materials required to
construct plank slushing floors and gob fences.
In the mid sixties , mechanization of cut and fill
mining wa s started by the scooptram. There were no changes
made to the stope-pillar geometries. There was a signifi
cant change in sequencing in that it became necessary to
change from a sloping sequence line to a series of steps,
with each step consisting of the 4 or more stopes making up
GROUND CONTROL AT !NCO 9
a mechanized unit. The lead unit approaches the leve l above
in an essentially flat multiple stope front (Figure 3).
In the seventies , in several areas, the primary
mining recovery fac tor was increased hy increasing the
stoping span or reducing the pillars or a combination of
the two approaches.
3. OBSERVATIONS
The following observat ions of ground behavior
associated with transverse and l ongitud ina l cu t and fill
mining we r e made by the author from the year 1960 to the
p r esent time . The observat i ons pertain to a number of
fnco's Sudbury area mines at depths ranging from 1500 to
6600 ft. below surface. The term, yield, refers to any
case where pillars undergo non-violent stress relief.
1. There is some critical height at which a narrow rib
pillar wi ll fail by yielding.
2. Pillars hurst if failure occurs before the crit ical
he ight is reac hed.
3. Back conditions in the stope generally improve when
the adjacent rib pillars experience initial failure.
4. The lead stope in a normal sequence experiences the
highest concen t ration of stress i n the crown area and
at a lower elevation than is the case with adjacent
stapes (figure 4).
10 p, H, OLIVER
(.!) z z ::E
0 0 :X: tw ::E ..J ..J
LL.
w (/) 0:: LIJ
~ z <( 0:: 1-
0 w N
z <( :X: 0 w ::E <(
GROUND CONTROL AT INCO
ILl z 0 N
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11
(/)
LtJ Q_
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c LLI 0::: LtJ 1-z :::> 0 (.) z LtJ
LLI z 0 N
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12 P, H. OLIVER
5. Af ter several stopes have mined up through the crown,
the effects of high horizonta l stre sses disappear
provided the footwall to hangingwall d imension exceeds
some cr itical value.
6 . Where the foo twall to hangingwall span is less than
some critical dimension, repetitive cro1m bursting
occurs as each stope approaches the level.
7 . The addition of cement to t he hydraul ic fill stiffened
the rib pillars and significantly limited the latera l
expansion of the ri b pillars.
8 . Increased compress ive shear arching took place at one
mine following the introduction of cemented sandfill.
9 . Stoping span reductions are necessary for mining
through the critica l crown region.
10 . Longitudinal cut and fill stopes could be mined w)th
low arch where mining widths ranged from 30 to 40ft.
Beyond 40 ft., increased mining widths meant an
increased frequency of joint oriented unpredictable
ground falls.
11 . In areas where multiple stapes are silled simultan
eously for mechanized mining, all of the pillars fail
at a common height. Failure is by burst ing if it
occurs during the mi ning of the first and second cuts.
Non -violent failure occur s if the onset of pillar
yield does not begin until the third cut is mined.
GROUND CONTRO L AT INCO
12 . The burst type of rib pillar failure in mechan ized
mining occurs at depth. At shal lower hor iz ons,
failure is by non-vio l ent yie ld.
13
13. The nature of the violent failure of rib pillars in
deep mining can be changed by destressing the ribs
as silling progresse s, but the degree o f damage to
the rib pillars a t the time of failure is almost
identical to the case where the pil lars have not
been des t ressod.
14. Where ri b pillar failur e occurs during the silling
phase of a mechanized unit at depth, fail ure is not
progressive with s illing . Some critical minimum area
must be silled before failure occurs . The urea of
failure t hen takes i n most of the silled unit, with
the l evel of damage highest in the central area and
with little to no damage clo se to the a butment s.
Damage is confined to the rib pillar walls and
shoul der s. There is no back damage .
15 . An i ncrease in the stoping extraction r atio, wi thin
limits, leads to a reduction in the height of induced
compress ive shear arch ing of the st ope backs .
16. Where the primary stoping ext r action r atjo is c l ose
to the optimum, localized pillar weaknes ses can l eau
to the development of horizontal fra ctures above the
back of the stope and above t he pillar. Blocky falls
of ground are liable to occur in t ho vicin i ty of
14 P , H. OLI VER
weakened pillars.
17 . The lead unit of a mechanized cut and fill sequence
can, under the right circumstances, mine up into the
critical crown failure region in a flat front and
cause the crown to yield rather than burst.
18. The stress level at the center of one pillar was
measured just prior to yield failure and was found
to he in the order of 4000 psi., as opposed to the
20,000 psi . uniaxial compressive strength of the
pi llar material.
4. HISTORICAL CONCEPTS OF GROUND CONTROL AS APPLIED TO
TRANSVERSE CUT AND FI LL MINING
4.1 Field Stresses
It was assumed the principal stress was vertical and
related to overburden weight. Some consideration was given
towards the possibility of hydrostatic loading to explain
the stresses in the crown pillars.
4.2 Yielding Pillars
Ground control practices revolved around the concept
or using yielding pillars and sequenced mining. Yielding
pillars were weak pillars and incapable of supporting the
superi ncumbent load; therefore the major part of the
superincumbent l oad was t ransferr ed to the perimeter of the
mined area. The yielding rib pillars supported only the
GROUND CONTROL AT INCO 15
immediate ground above the stope back.
A yielding pillar was considered to be a narrow
pillar, generally less than 30 ft. wide. Any pillar wider
than 30ft. was considered to be strong and liable to
burst.
4.3 Sequence
Sequencing controlled the gradual enlargement and
subsequent merging of the individual level stress domes.
The sloping sequence line limited the volume of ground
contained in the critical crown failure region by creating
a wedge shaped crown with just the tip of the wedge in the
critical crown bursting zone. The tip could either yield
or fail in a series of small rockbursts. Small rock rem
nants were slotted through to eliminate a source of major
rockbursts.
5. THE NEW CONCEPT Or GROUND CONTROL
The historical concepts of ground control offered
satisfactory explanations for parts of the observed pheno
mena. However, with ever deeper mining, the mechan1zation
of cut and fill operations which altered sequencing, and
experimentation with varying stoping widths and primary
extraction ratios, it became increasingly apparent the
concepts were incomplete because of the faulty assumption
16 P, H. OLIVER
of superincumbGnt loading .
5.1 Field Stresses
Deeper mining provided a clue as to the nature of the
field stresses through ground behavior in development
openings. ll igh horizontal stresses were inferred and
subsequently verified by stress measurements. The principal
stress is near horizontal and in the areas pertinent to the
listed observations strikes roughly parallel to the errup
tive contact or norma l t o the di rection of transverse fill
mcthoo mining. The least stress is near vertical and in
line with superincumbent loading. Details of the study arc
covered in the paper by llerget et al (l) which was prepared
for presentation at this Symposium.
5.2 Controlled Sag Alleviates llorizontal Stresses
The established fact of a high horizontal field stross
state explained the high stresses encountered in cro"~
pillars and the behavi.or of the cro1vns at various stages or mining. High horizontal stresses confused the picture with
respect to the improved stoping conditions associated with
pillar yield until it was realized the concepts of back
deflection (sag) related to stope span and pillar yield,
~s out I i ned hy J . Parker (3), could be applied to trans
verse cut and fill mining. While Parker's (3) concepts
GROUND CONTROL AT INCO 17
were developed from observations of the behavior of
openings in a room and pillar mining operation of a near
flat, tabular depo sit, they were based on guidelines out
lined by C. L. Emer y with respect to the behavior of beam
columns.
The deflection of the back of an opening, if down
ward, sets up a horizontal tensil e stress component which
will, depending on the deg r ee of deflection, offset high
horizontal compressive stresses in the back of the opening.
If there are a series of openings separated by yielding
pillars, there will be an overall abutment to abu tment roof
sag which will effectively reduce horizontal stresses jn
the backs of the openings even though the spans of the
individual openings may be too narrow to provide stress
relief by themselves. The height of the openings is
insignificant towards stress relief outside of the relation
ship between pillar height and yield.
Horizontal stre ss relief through back sag explained
phenomena related to span and yield. It explained why
stoping ground conditions improved when the pillars yielded;
why severe induced arching occurred i n narrow open i ngs
while little to no arching was evident in adjacent,
moderately wide openings; why tensile conditions were
common to very wide openings. It explained why ad justing
the primary stoping recovery factor by slott ing out parts
of the ribs could lead to improved back conditions and if
18 P, H. OLIVER
carried too far to tensile back conditions. lt explained
the relationship between local pillar weaknesses and
localized tensile back conditions.
The relationship between sag and the stress state of
the stope back points out the importance of distinguishing
the nature o( the ground problems ln a working place.
Induced compressive shear arching can be alleviated by
increasing the stoping span, by increasing pillar yield
through reducing pillar width or by a combination of the
two approaches. Tens ile back conditions, characterized
by unpredictahle, joint oriented falls of ground, are
indicat ive of excessive span, excessive pillar yie ld, a
combination of the two, or the lack o f elevated horizontal
field stresses. Where the condition can be traced to
excessive span or yield, conditions can be improved by
reducing span, hy increasing the pillar width to reduc e
yield, by decreasing pillar yield through improved lateral
support, or any combination of the above approaches.
A wrong assessment of the nature of the ground
problem can load to a worsening of the condition. The
miner's rule of thumb approach oC reducing span when
difficult back conditions arc encountered is wrong when the
condition is characterized by induced compressive shear
arching.
GROUND CONTROL AT INCO 19
6. YI ELD
6.1 A Definition of Yi eld
Yield is considered to be any case where moderately
to highly stressed ground undergoes stress relief in a
non bursting manner.
6.2 Yield As A Rockburst Control Mechanism
Inco has been using sequencing to alleviate rockburst
conditions for 34 years. Observations noted earlier in
this paper and which pertain to crown pillars indicate that
crown pillars can be made to yield under the corr ect
circumstances in spite of their being the reve rse case to
rib pillars. Rib pillars have constant width and
increasing height, 1vhile cro1vn pillars have constant height
and decreasing width (Figure 5). Under favourable
circumstances, both rib and crown pillars can be made to
yield and under less favourable circumstances, both pillar
types will burst.
It has been concluded that yield is the prime
mechanism of rockburst control and that sequence i s a means
to establish conditions favourable towards yield. The
successful applicat i on of sequencing at !nco' s Sudbury
operations is felt to be due in a large part to the widths
of the orebodies which. have contributed a key element to
the yield phenomenon.
t :_:-_;_:.:.J r-:.:-~::::·.<:t t:::~::Y.} :f 1>\':.:·<-t 1/::?::::t L2J LDJ LiJ L2J Ld rrm ~ LillJ ~
SIGNIFICANT STRESS. DIRECTION
I • H CROWN I PILLAR .. I
ii . . .
SIGNIFICANT STRESS
DIRECTION
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N 0
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GROUND CONTROL AT !NCO 21
6.3 The Unknowns of Yield
Current literature does not offer a suitable
explanation for the yield phenomenon. 1 t provides neither
a means of determining the parameters governing yield,
in~luding the influence of lateral restraint, nor does it
provide a means of determining post-yield properties. The
lack of understanding of yield phenomena has deferred
mining improvements as a result of the necessity to use
trial and error in developing methods for utilizing yield.
The problem with trial and error, in the absence of theory,
is that once something works, experimentation tends to
stop. The factors which make the system work are not
understood and the effects of subsequently changing one or
more of the factors may not be recognized.
lnco continued with the S set stope, 4 set pillar
geometry, above the 4000 ft. horizon, through to the end
of the sixties, although the support nature of the fill
changed twice, to hydraulic fill in the early fifties and
to cemented hydraulic fill in the early sixties. Experi
mentation with increased stoping spans and primary mining
recovery factors did not begin until the seventies. That
the results were favourable was credited to differences in
conditions between· the areas of mining Hith increased
primary recovery factors and past areas mined with conven
tional geometries. The one identifiable unique change in
22 P , H. OLIVER
condjtions ls that of increased pillar rigidity associated
with the use of cemented hydraulic fill.
6.4 Suggested Parameter s Governing the Beha~i~~!
Yielding Pillars
The Inco experience with yield has demonstrated the
importance of yield as a mining tool. It has not, however,
been poss ible to develop hard and fast rules for the design
of yielding rib and crown pillars. Observations of yield
behavior indicate the accepted means of calculating
critical pillar stress do not apply in the case of yielding
pillars.
It does appear that a yieldjng pillar might be
defined as one having a width to height ratio of 0.5 or
less. The width to height ratio, may in some cases, be
greater than 0.5, but it will never be greater than unity.
Pillars appear to behave in a like manner to columns,
except that in the case of rock pillars in comparison to
steel columns, the slenderness ratio effect on instability
is greatly increased; possibly because of the lack of in
situ tensile strength.
It is suggested the curves developed from the
Generalized Euler or Tangent Modulus Formula for columns,
plotting critical stress against the slenderness ratio,
may parallel measured values for rock pillars except that
the slenderness ratio at the proportional limit will
GROUND CONTROL AT !NCO 23
correspond to a W/H ratio of hetween 1.0 and 0.5 (Figure 6).
It is significant that .should this hypothesis prove valid,
a yielding pillar will be similar to a long column up to
the point of critical stress. The critical stress level
will he a function or the elastic modulus and the slenuer
ness ratio and not a function of the uniaxial compressive
strength as is the case with current pillar strength
theories.
It is hoped the recognition of the importance of
yield with respect to safety and economics will stimulate
research into yield phenomena no1v that such research has
been maue possible through stiff testing machines. The
behavior of pi liars .should he studied to determine the
relationship bet\veen critical strength and the l>l/11 ratio;
post yield physical properties; the effect of lateral
restraint on the crit.ical strength anti post yield properties
with particular emphasis placed on the role of fill with
respect to rib pillars and yielding rib pillars with
respect to crown pillars.
7. FTLL
Fill is considered by the majority of mine operators
in Canada to be primarily a working platform and secondarily
a medium \vhich limits the volume or open ground in a mine.
Inco experiences with three types of fill in transverse fill
method mining, backed up by the new understanding of the
C/) C/) w a: ..... C/)
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..... ir (.)
hort
I-HYPERBOLA \ \ __ .\..- _ ,--...:!!ELO POINT
\ ----------\
,-PROP· LIMIT
Lon
SLENDERNESS RATIO ~ - COLUMNS
1. ;~~~~ ?~- ?. ...=.; -- YIEc;,NG --T ·0 0 ·5
WIDTH/HEIGHT RATIO ~ - MINE PILLARS
FIGURE 6· SUGGESTED RELATIONSHIP BETWEEN COLUMNS a MINE PILLARS
N .J;:::
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GROUND CONTROL AT INCO 25
role yielding pillars play towards controlling stoping
ground conditions suggests the need to review the role
played by fill. The parallelism, although somewhat delayed
between improvements in the fill characteristics with
respect to rib pillar support and improvements in fill
method mining economics related to reduced back support
requirements, increased stoping spans and increased primary
recovery factors, is too distinct to be ignored. There is
a possibility the point of diminishing returns has not yet
been reached and further economic benefits may still be
possible through the use of stronger fills.
8. CURRENT AND FUTURE PLANS
8.1 Current Transverse Cut and Fill Layouts
The understanding of the mechanism of roof sag
towards controlling horizontal stoping stresses has been
too recent to have influenced current mining layouts. The
present variations in stope-pillar geometries, ranging
from stopes 22 feet wide with 14-foot rib pillars to
42-foot stopes and 18-foot pillars (the dimensions include
overbreak), are being assessed. A flexible approach is in
order until such time as more specific design parameters
become available.
APPLICATION OF HIGH-SPEED PHOTOGRAPHY TO ROCK BLASTING AT CANADIAN INDUSTRIES LIMITED
A REVIEW
29
S . Chung 1 , !L Mohanty 1 , L.G . Desrochers 2 , a nd I..C. Lang3
Abstract
The role of high-speed photographic techniques in studying and opt i miz i ng blasts in open pit mines is reviewed. Among the qualitative data obtai ned through these studies are f i ring sequence, occurrence of miss holes , the degree of confinement of stemming and natura of muck p i le formation. The quantitative da ta includes velocity of fly r ock , spalling stress and heave energy r equired for muck pile f ormation. A t ypical c amera and playback sys tem and field procedures for photographing blasts are described. lt is found that the uplifti ng velocity 'V' on t he bench during the gas expansion stage of a blast obeys a s imple power l aw for c yl j ndrical charges,
V Klw~~ 2 ~-n' R being t he distance and
'W' the charge weight. For blasts in i r on oro format ion 'n' is found to be ne arly equal to uni ty . For large open pit blasts the veloci ty of fly rocks is about 15 m/s whereas excessive l y loaded boreholes may result i n fly rock velocity of 50 m/s or higher. 1Research Physicist, Explos1ves Research Lab . ,McMas terville 2Research Scientist, Explos ives Research Lab.,McMas terville 3Supervi sor, Appli ed Blasting Research, Tec hnical
Marke ting Services, Explosives Div i s ion, Montreal. Que.
30 CHUNG ET AL
1 . iNTRODUCTION
The us e o f h igh spcccl photography in s tudying
s hor t - lived phenomena is not new and its pr i nc i ples a r e
well estab lished. The range of high speod photography
may va ry f rom a f ew doz en frames per second with time
r esolution of the order of seve r a l mi lliseconds t o over a
million frames pe r second wi th t ime reso lution in the
sub-microsecond range . This pape r is conce rned with t he
app l icat i ons i n the medium- high speed r an ge i.e. in the
1 00 ~2000 f r ames per second, in the f ield of rock bl asting.
The first comprehensive studies on the usc of a
high- speed camera in b l asting studies were ca r r ied out a t
the U.S . Bureau of Mines (Bl air, 1960). Vari ous photo-
graphic techniques ha ve been in use for over a <lecade a t
Canadian Industr ies Limited in assessing blas t results,
bu t since t he early seventies high - speod photograph ic
studies have forme d a n integral part of roc k blasting
research at the CIL Dxplosives Res earch Laboratory. The
r es ul ts f r om these studi e s are routine l y used to confirm
blasting predictions and prov ide added insight on the
mechani sm and geometry of blasting (Lang a nd favreau, 1972;
van Zeggeren and Chung, 1973) . Th i s pape r r eviews the
princip l es , field procedure s and genera l app lications o f
high-speed photogra phic studies a t CIL. Th i s is fol lowed
by a p ic ture show of typ ical blasts as recorde d by the high- s peed camera.
HIGH-SPEED PHOTOGRAPHY AT C. I.L,
2. DESCRIPTfON Of F.QlJIPlvll.:NT
As shown in Figure 1, the filming system consists
of a LOCAM Camera equipped \vi th an automatic exposure
control unit, a junction box and a portable electric
power generator. The camera operates on liS VAC 60 Hz.
The frame rate is adjustable for any rate bet\veen 16 and
SOO frames/se~ond with an accuracy of ±1% or ±l frame;
31
the film used for blasting studies ls Kodak high speed
(160 ASA) 16 mm EKTACHROME Type 7241 EF 449. Accessory
lenses ranging from 16 mm to 150 mm are available to cover
a wide range of field of view.
Also installed inside the camera compartment is a
heating element for usc in cold weather. Since this camera
consumes not more than 300 watts, a lightweight !londa
portable generator Model 300E can supply enough power to
run the system.
The function of the junction box is to control the
camera operation; to start the camera by breaking the
trigger wire and to switch off by a built-in timer.
At maximum frame rate (SOO fps), the camera will
not consume more than 10 feet (or 400 frames) of film
to accelerate; therefore at a frame rate of 300 fps it
is sufficient to give 4 seconds for the run up, 6 seconds
32 CHUNG ET AL
LOCAM CAMERA
AC!DC CONVERTER
TRIGGER BOX
JUNCTION BOX
PORTABLE POWER GENERATOR
..._ __ 120 V ( AC)
FIG.1 PHOTOGRAPHIC SYSTEM
HIGH-SPEED PHOTOGRAPHY AT C, I ,L,
for recording the blast action and about 4 seconds for
taking the panoramic view after blast.
3. FIELD PROCEDURE
33
To Cilm a blast, tho camera must be properly located
and protected by a shelter . For example, in the case of
filming the face movement a suitable location would be
on one level above, 600 to 800 feet away and looking at
an angle o[ about 30° to the face (Figure 2). At least
four visible targets (.S x .S m2 ) arranged in three groups
are hung over the crest and rested on the bench face; in
the case of filming the top of the bench, a group of at
least nine targets are placed behind the last row or on
the side adjacent to tho blast. All these markers, as
well as the camera location, are painted and surveyed
into a blast plan for use as dimensional controls in the
film analysis.
The trigger wire of the junction hox is connected
to the blast initiation with no delay while a long delay
(about 4 seconds) is placed between the trigger and the
blast.
4. APPLICATIONS
Both qualitative and quantitative information can
be ohtained from high speeu photographic studies. The
qualitative data which may include information on the
34
TOE
CAMERA DIRECTION
CHUNG ET AL
& & &
tv1ARKERS
FIG. 2 CAMERA VIEW
HIGH- SPEED PHOTOGRAPHY AT C, I , L,
firing sequence of multiple row blasting and correlation
with respective delay periods, location of miss holes,
degree of confinement by stemming and initial r ock move
ment can be of immediate benefit to blast design and
planning. ln addition, the colour of escaping gases may
also indicate possible deflagration or changes in the
explosive composition.
35
The high speed photographic technique i s particularly
sui ted to quanti tative measurements of a large number of
parame ters for improved blast efficiency. The accuracy
of measurement is controlled only by t he time resolut ion
of the camera and the dimensional controls such as markers
or grids on the bench. The measurements include particle
velocity on the bench face, and hence the spalling strength,
the time of critical rock movement on the bench fac e,
velocity o f fly rocks, the uplifting velocity on bench top
near adjacent holes, determination of delay time fo r
opt imum rock movement, fragment size, estimation of requi red
heave energy from the rock mass motion and estimation of
borehole pressure at the instant of ejection of stemming.
The las t two parameters arc of particular importance in
predic ting explosive action and blast patterns in r ock
through analytical models.
36 CHUNG ET AL
5. DATA ANALYSIS
The processed film is played back through a L-W
Photo-Optical Analyzer (Model 224-A) for visual inspection
of the entire blast. For a more critical examination and
measuremen t of displacement of a particular target at a
given time, the fil m is played back frame hy frame. Since
a pre -set scale system is set up on the bench and on
bench face by means of markers, tedious methemat ical con
version process in obtaining the true displacement values
is largely e limi nated . 1~e inclination of t he opt ic axis
due to camera locat ion and the possibility of ta-rget moving
off non-parallel to the film plane arc ta ken into account
in determining displacement; the l atter is accomplished
by averaging. The accuracy of displacement measurement is
estimated to bo 10%.
A cross-section of the bench with markers (M) is
shown in Fig. 3 . A typical blast pattern for an open pit
mine in hematite ore formation is shown in fig. 4. Tho
corresponding displacement vs. time curves are shown in
fig. S. In this particular case the velocity of free face
is considerably larger than that on top of the bench. The
initial large scale rock movement on the bench face occurs
at a bout 100 mscc. after blast initiation and at about
200 msec. on top of the bench for the pa ttern and delay
shown in Fig. 4.
HIGH-SPEED ~IOTOGRAPHY AT C,I,L, 37
H
FIG.3 BENCH CROSS SECTION
38 CHUNG ET AL
(./) (/)
E E t[) LO M ~
I I z ~ X lf) .. 4: w lf) _j a: >- (L u <(
_j
1-w n:: l/)
W\ <( 0\ _J t- \ co
\ ~ .
• l9 LL
\
E
:] <( • 0::
w w ... _j 2 ... lf) <( <( ~ a::: u u w 1./) ~
n:: <(
2
HIGH-SPEED PHOTOGRAPHY AT C.I.L. 39
....... Ill
.S z 0
at-10~ N!::
z
~\ t- LaJ V)
<t: ~ ...J m a: 1-w t- U) IJ..
t, 0<( > ow ,, N2: 1-t t- z \ UJ \ ~ \ IJ.J
0 0 <( I{) ...J ~
Q.. (/)
c •
10 (!)
LL.
N ~
(w) Nl91~0 ~01::1~ !N3~3:)'VldSia 0
40 CHUNG ET AL
Fig. 6 shows variation of uplifting velocity on the
bench top vs. scaled distance (R/Wl/ 2 ) in another iron
ore mine. 'R' is the distance (m) [rom the centre of
gravity of the explosive column and 'W' is the total charge
weight (kg). It is seen that the data can be fitted
empirica l ly by the fol lowing:
R :·n V ~ K ~ , where K = 2 .24 and n ~ 0.93. The
1\fV 2 ,
constants 'K' and 'n' are characteristic parameters for the
particul ar explosive- rock combina tion and inc lude atten
uation and geometrical spreading factors. Thus from a set
of data obtained from film analysis the particle velocity
at any point on the bench may be calculated. An important
blast design parameter which can be estimated from these
velocity values is the absolute maximum permissible delay
time for the nearest delayed shot. This is the time for
maximum extension which a section of detonating cord in
the delaye d borehole can sustain before failure . Ilowever,
caution mus t be exercised in estimating particle velocity
from the bench top to that of the bench face as different
conditions provail for the two geometries as shown in ~ig. 5.
Typ ical flyrock velocities for an iron ore mine are
shown in Fig. 7. These velocities are much higher than
normally encountered i n blasts of proper design . The se
figures also show subsequent increase in flyrock velocity
9.
5.
-54. >
HIGH-SPEED PHOTOGRAPHY AT C,J,L, 41
.3 .4 .5 .6 .7 .8 .9
SCALED DISTANCE (m/kgV2.)
FIG. 6 UPLIFTING VEL. VS SCALED DISTANCE
42 CHUNG ET AL
-
q Ill 0 Ill
(~) Nl91~~ 11\!0~.:J ~3~3 :)\ffd SIO
0 0 ..-
....... Ill
o-5 I{)
z 0 1-<(
i= o -z o-o t-,_ (/)
<( ...J m 0::
ow I() I-
u. <(
w ~ 1-
0
w _J
LL 0 a::: 0...
~ u 0 0::
>_J
LL
"' <D LL
HIGH-SPEED PHOTOGRAPHY AT C,J,L, 43
due to multiple collis i ons.
6. CONCLUSIONS
The high-speed photographic technique is a simple
and direct means of studying blast results in open pit
mines. In current open pit practices, frequently involving
over 100 ktons of rock per blast, proper selection of
explosive and optimum design of blast patterns i s of
crucial importance. High - speed photographic studies
provide both qualitative and quantitative data for greater
blasting efficiency and avoiding costly errors. As a
research tool such photographic studies can provide
important data on explosive energy partition, determination
of optimum delay between rows and general verification
of theoretical blast predict i ons.
44
Blair , l3.E.,
CHUNG ET AL
7 . Bl BLI OGRAPHY
"Usc of High - Speed Camera in T\lasting
Studies", U.S. Rureau of Mine s,
RI-5584, 1960.
Lang, L.C. and Favreau, R.F., "A Modern Approach to
Open-Pit Rlast Design and Analysis",
(ClM) Bulletin, June 1972, pp 37-~~-
van Zcgge ren, F. and l.hung, s., "A Model for the
Prediction of fragmentation, Patterns and
Costs in Rock Blasting", Proceedings
15th. Symposium on Rock Mechanics,
Rap id City, South Dakota, 1973.
45
SLOPE MONI TORING AT BRENDA MI NE
LES PROBLEMES POUR SURVEILLER DES PENTES DE LA MINE BRENDA
Abstract
G. Blacklvell* D. Pow** M. Keast***
The problem of monitoring slopes at a part icular mine are discussed. Methods of measur i ng wall movement are examined and the combination of elec tronic distance measurement and theodolite angular measuremen t chosen. To decrease the requ ired manpower, an elect ron ic geodimete r combining both functions was bought.
In its simplest form of operat ion, the distances are measured to ±6 mm and angles to ±5 sec. By using more sophisticated techniques, distance errors can be reduced to ±2 mm. The cost of good reflecting targets is such that a method of utilizing inexpensive short range reflec tors was developed .
*Mine Engineer **Junior Mine Engineer
***Technician Brenda Mines Ltd., Box 420, Peachland, B. C. Canada
46 G, BLACKWELL~ D, POW AND M, KEAST
The accuracy of the machine is found to be quite adequate for monitoring failing areas.
Resume
Los problemes pour surveiller les pentes d'une mine particuliere sont discutcs. Les methodes pour mesurer le mouvement des parois sont examinees. La combinaison de la mesure electronique de distance ct de la mesure angulaire avec theodolite a ete choisie. Pour diminuer la main d'oeuvre requise, un geodimetre incorporant les deux mesures fut achct6.
Dans sa forme la plus simple d'operation les distances sont mesurees ~ ±6 mm et a des angles de ±5 sec. En utilisant des techniques plus sophistiquees les marques d'erreur peuvent @tre reduites de ±2 mm. Le coOt de cibles qui r6fletent bien est tel qu'une methode utilisant des reflccteurs a courte distance et peu coOteux fut developpec.
La precision de cette machine fut trouvee suffisante pour surveiller les zones instables.
SLOPE MONITORING AT BRENDA MlNE 47
1. INTRODUCTION
1.1 Brenda Mine
The Brenda open pit is located 26 miles west of
Kelowna in the southern interior of British Columbia. The
mine elevation is 5000 feet ab ove sea level . Temperatures
range from a minimum of -30°C to 30°C with freezing con
ditions experienced from mid-September to mid-April during
which an annual snowfall of 400 - 800 em is experienced.
A low grade copper -mo lybdenum ore is mined at the
rate of about 27,000 tons per day with a similar amount of
lower grade and waste materia l being stockpiled. A frac
tured quartz diorite rock gives a competent north wall and
good east and west walls. The low grade nature of the
deposit dictated a mine plan consisting of several pits
ins ide each other . Pit One is nearing complet ion. I ts
north and east walls are being removed as Pit Three deepens.
Pit Four has just commenced and will eventua lly produce new
walls all around as shown in Figure 1.
1 .2 Slope Monitoring Considerations
With wall heights in the order of 1000 feet planned
for the fu ture , management thought it wise t o have a simple
ye t effect ive method of monitoring the se walls, to determine
i f movement is occurring and if f ailur e was imminent.
48 G, BLACKWELLJ D. POW AND M, KEAST
N
I 0
I 0
Pit (4)
Pit (3)
S o
Pi t (1)
oz
0 3
fiGURE 1
600 Ft
I 180 t-1
6
To~ Backsight
SKETCH PLAN OF PIT SHOWI NG SURVEY STATIONS
SLOPE MONITORING AT BRENDA MINE 49
An investigation of the different methods availabl~,
their costs and manpower requirements when applied to the
Brenda operation was made. Basically there are three
methods available:
a) Deformation in a borehole
b) Photogrammetry
c) Surveying
The costs of any system are roughly proportional to
the degree of accuracy required. Figure 2 shows the relat
ionship between cost and the amount of movement easily
detected. This data only applies to the Brenda operation
and does not go into details of capital and operating
costs.
For an unlimited sum of money, any movement can be
detected. Published literature1,2 indicates a wide range,
from inches per month to inches per day, of movement during
a slide. Some movement must occur due to the blasting and
removal of vast volumes of rock which is of no immediate
concern. However, unstable movements must be detected
early enough to give management sufficient time to alter
the mining plan or preferably, time to consider stabiliz
ation of an area.
50 G, BLACKWELL~ D. POW AND M, KEAST
500
'\ EXTENSOMETERS
'\
" 0 OTH~ BOREHOLE 0 0 ...... DEVI'cES >< '\ - \. BE1'TTIR -::;:: so ' I.J..l EDM'S !- '\ (/)
>--(/) '\ r.r. EDM + THI:-<{DOLIH 0
f- '\ (/)
0 PHOTOG~ffiTRY u
'\ EDM
\.
TII~DOLITE
" 5
0.3 3.0 30.0 300.0
MI l.l.IMETERS OF MOVEMENT DETECTED
FIGURE 2
SOt-11:: METHODS, ESTIMATED COSTS AND ACCURACIES
OF SLOPE MONITORING SYSTEMS
SLOPE MONITORING AT BRENDA MINE 51
The system selected should require a minimum of man
hours for the collection and analysing of data. It would
be beneficial if the direction of movement was detectable,
as this might indicate which fault plane should be strength
ened if stabilization was to be carried out.
The choice of a system is limited by the mining
method. Only the final wall can be adequately monitored
using boreholes. This increases the cost and accuracy but
gives no indication of how ear lier pit walls are standing .
Photogrammetry would not provide instant information unless
the analysing system were installed at the mine. Even so,
it would probably take considerable survey time to obtain
the co- ordinates of set up and target points . This leaves
survey methods as the final choice .
1.3 Survey Monitoring
As a simple example , the movement of a point around a
one foot cube was simulated by sightings from three points
3000 feet away . Neither triangulation nor trilateration
would indicate all movement . However, a combination of the
two methods would indicate a one inch movement rela tively
easily. If instrument stations were set up to the best
advantage, the amount of movement detected would be limited
only by the machine accuracy.
52 G, BLACKWE LL1 D. POW AND M. KEAST
The most inexpensive approach was to use the t heodol
ites already available at the mine in conjunct ion with an
electronic distance measuring unit (EDM). Many EDM's were
examined and several were tes ted at the mine site. Tho
helium-neon type was not thought to be better or worse than
any other , but was re latively inexpensive and utilized a
visible red light beam.
Manpower requirements for this system would be l a rge
because of the number of readings required with the theodol
ite. To measure distances t he EDM is then mounted on the
tr i-brach and further readjngs taken. Data analysis would
be an equal problem in terms of man hours.
AGA suggested that their Geodi meter 710 would a l l
eviate t he se problems, but at a greater ini tial capi ta l
expense. Looking to the future it would be reasonable to
assume that routine mine surveying \vOuld be automated to pro
vide maps, etc. directly from recorded instrumen t data. A
combination of the AGA Geodat 700 punch tape recorder and
the 710 Geod imeter would reduce manpower requ irements and
instrument time. Monitor i ng and routine survey wor k would
be a combined operation with data and maps presented in
comp l ete form from the Geodat punchtape.
SLOPE MONITORING AT BRENDA MINE 53
A telephone conversation with Dr. D.G.F. Hedley at
the Department of Energy, Mines and Resources confirmed
that the instrument would meet the manufacturers specific
ations in most respects.
Management then decided to purchase the 710 Geodi
meter after demonstration.
2. A BASIC MONITORING SYSTEM
2. 1 Stations
Having concluded that surveying would provide most of
the slope monitoring information required, concrete survey
stations were installed around Pit 3 in the summer of 1974.
These stations were made of weld mesh, rcbar and old
grinding rod. "Ready Rod" was welded to the rebar to hold
an instrument platform. Concrete was poured into a 3 foot
diameter cardboard mold around the reinforcing structure.
A brass platform and forced centering bolt were added
later. Figure 3.
Five main stations were set around the pit walls, and
a further station outside of the influence of the pit was
added to provide a stable backsight for all five main
stations. With the arrival of the Geodimetcr in December
1974, basic monitoring commenced with the surveying of the
main stations.
54 G, BLACKWELL, D, POW AND M, KEAST
2.2 Using the Geo~imcter 710
Table 1 gives a brief description of the instrument.
There are two main parts, the measuring and display units,
joineu by an electrical cable, Figure 4. A full descrip
tion is available from AGA3 •4 . Briefly, angles are meas
ured by means of horizontal and vertical pulse discs. 1he
relative position of tracks on the discs is converted
electronically to angular position.
Distance measurement is accomplished by determining
the phase difference between transmitted and reflected
light heams. Frequency (1) finus the nearest S metre,
frequency (2) the nearest 0.001 metre. Frequency (3) is
used to solve units of 250 metres up to 5000 metres.
The beam is reflected from either a cube corner glass
prism ($50- $200 each) or a plastic reflector ($2- $5 each).
Alignment of the prism can be 20° off, but the plastic
reflector loses range quickly as the face is turned away
from the beam. Returning signal strengths can be estimated
using the meter on the display unlt. Adjusting the angular
verniers and beam expander to give maximum signal strength
is a useful aid when measuring distances.
The display unit automatically gives various combin
ations of slope, horizontal and vertical distances with
horizontal and vertical angles as required.
SLOPE MONITORING AT BRENDA MINE
TABLE 1
AGA 710 Ceodimeter
Cost $22,000
Weight (including carrying
Power
Distance Measurement
Expandable 1 mW He Ne gas
Modulation Frequencies FI r-z F3
Range 1 AGA prism 1 plastic reflector
Resolution
Angular Measurement
case) 25
12
laser
299.7 K Hz 29970 30000
1700 Ja
200 m J mm
K Hz K Hz
(1 mile) (600 ft)
Erect Image 30X magnification
kg
V.
Resolution Horizontal Circle 1 sec Vertical Circle 3 sec
55
(55 lbs)
DC
56 G, BLACKWELL, D, POW AND M, KEAST
~ U.l E-< U.l ~ ....... Q
0 IJJ 0
..; 0 -<
""' IJJ .:X: :::> 0 ..... u.
' '! ' • .. I
;:··,
7. 0 ..... E-< ..; E-< (/)
>< IJJ > c.: :::> U)
"" w c.: ::::> (.!) .. ...... u.
SLOPE MONITORING AT BRENDA MINE 57
Since the machine utilizes the laser principle, eye
safety must be considered. The one milliwatt laser emits
an average power of 0.125 milliwatt per square centimetre
and should not be stared at from a close range. The normal
human reflex is to turn away from the visible beam and
therefore the machine is considered safe when used as
directeds.
Safety precautions are incorporated in the machine
and Brenda has undertaken others:
i) The laser beam is turned off when not
required, e.g. when first sighting a nearby
target through the telescope.
ii) There is a filter which is used when
operating at short ranges.
iii) All mine operating personnel have been
given a safety talk on the machine.
iv) Survey personnel are provided with safety
goggles which do not transmit the red
light.
v) Warning signs are present which tell the
reader not to stare at the beam.
2.3 Factors Affecting Machine Accuracy
The beam is affected by the density of the medium in
which it travels. A correction is therefore necessary for
58 G, BLACKWELLJ D. POW AND M, KEAST
the variations of air pressure, temperature and humidity.
The correction factor is obtained from a table and dialed
directly into the machine. Over a distance of 1000 metre,
about 1 mm error would he caused by an error in the temp
erature reading of zoe, at constant pressure. Humidity
changes have very little effect on red light.
Patches of warm and cold air over the beam path pro
duce erroneous results whereas overcast windy mornings or
nights produce the best results.
Measurements of pressure and temperature present
problems. In most stability work measurements over the
beam path are not always possible. The most practical
system would be to place a maximum/minimum thermometer on
a pole near the target and use an average of the target and
instrument conditions for calculating the correction facto&
Temperatures around the pit vary by ±zoe at any time
during the morning. Pressures vary due to elevation by
±r mm Hg. The error caused by these changes is in the tz mm range, but does not greatly affect monitoring data using
the same stations.
At Brenda it has been found that other climatic con
ditions, wind, cloud, snow and freezing rain have an effect
on the machines operations. The cloud level occurs at the
mino elevation during the winter months.
SLOPE MONITORING AT BRENDA MINE 59
Dense fog can remain at the mine level for several
days. GenGrally a reflection from a cube corner prism can
be obtained although the target itself may have just dis
appeared from view.
Wind tends to disturb the instrument, but the spread
of the beam is such that suitable distance measurements can
be obtained. Snow and rain tend to give a greater spread
of readings about a mean.
A major winter problem was the coating of the
reflectors in ice, up to 1/ 2 inch thick. This problem was
solved on a temporary basis by use of an insulated shield
with an open front face. A lZV lamp bulb heated the inside
of the shield and kept the reflector from freezing. The
complete winterization of the system will be completed in
75/76.
Unfortunately there was no target housing available
that was 100% sa tisfactory for mine purposes. For this
reason a housing was made in the mine shop consisting of a
2 1/2" pipe coupling, welding road and a 5/8" bolt.
Figure S. This housing is now standard at Brenda, and ful
fills all requirements.
60 G. BLACKWELL, D. POW AND M, KEAST
r:lGURF.. 5
TARGt:T HOUSING
rlGURE 1l
SOUTII WALL lli\UL ROAD
SLOPE MONITORING AT BRENDA MINE 61
3. IMPROVING THE SYSTEM
3.1 Routine Surveying From Main Stations
The initial system employed involved setting up on a
main station. Readings were taken to tho main stations,
and reflectors mounted in 3" holes drilled in the ro~.:k
faces were monitored. It was found that operators tended
to blas their distance readings instead of reading the
first reasonably stable number. At this stage the
manufacturers stated accuracy of ±0.02 feet was not being
attained. To overcome these problems, a regression
analysis procedure was adopted. Readings were taken at
various correction factors instead of dialing in the
correct one. Using the various correction factors and
distances a least squares equation was used to obtain the
correct value of slope distance. This reduced errors
significantly and gave the operators a better feeling for
the drift in readings.
At AGA's suggestion, the instrument was converted to
display metric distances. This solved the problem of
accuracy because it removed on electrical circuit and
stopped truncation of the last decimal of distance. An
examination of the data showed that four readings, two face
left and two face right, would be sufficient. The regress
ion method was abandoned in favour of dialing the correct-
62 G, BLACKNELLJ D, POW AND M. KEAST
ion factor as before. A plot of typical data is given in
Pigure 6; a spread of t6 mm is evident.
Angular measurements were taken using the reiteration
method6 on one quadrant. The instrument did not display
the po~itive action of the normal theodolite. Consequently
care had to be taken not to disturb the instrument after
sighting a target, e.g. pulling on the cable to the read
out unit. Typical data is given in figure 7.
All angles are meaned to about ~S second. The
scatter and standard deviations agree with those published7
for a 0.1 second theodolite.
It ~hould be noted that vertical angles are corrected
internally by an electronic plumh which is set during the
initial machine calibration process. face left and face
right angles must be taken since the instrument does not
hold its adjustment.
3.2 Normalizing Data to a Known Backsight
The error in day to day readings i~ from two main
sources, atmospheric conditions and internal machine error .
The atmospheric correction dialed into the machine may not
have been correct since temperature and pressure readings
cannot conveniently be taken at targets all around the
compass. Present practice is to use the temperature and
540.06 -
D. ~/ ' / " / ~- -~- -L:::.
D.
~ Unstable Station
540.04 () Backsight Station
SLOPE cr 0.006 (stable)
DISTANCES
(Metres) ~
546.62 -
546.60 () ~ 0 0 0 0 -----::-- 0 ' lS. 0 ~ _o _ __ o ~ ~-_-__=- ts -L'>-::_.~---:c,.:: _ __ 0 0 ()
546.58
0 I 5 ~ ---- 11 o
DAYS
FIGURE 6 TYPICAL SLOPE DISTANCE DATA
+2o
-X
"2o
(.()
r 0 -o m
3: 0 z --; 0 ::0 -z Gl
J> -;
0;)
::0 m z 0 > :s: z m
en V-1
-9°24'30"
-9°24'40"
-9°24'50"
-9°25'00"
5°40'20"
5°40'10"
5°40'00"--
/:),. b. --. - -/:),. /:),.
/
0
Jl-6
\
/:),.
D 0
0
Vertical Angle Unstable Station Horizontal Angle Vertical Angle Stable Backsight S seconds
6d8'00" o __ o .... ./,. 6~7 'SO" \ / b. __ /:),. ~ /
- . , .D. 64..,27'40"
Do ... D.,. ;,--... . -o .D..
......... . --0 64°37'30" ---b. D ./ /
o ..... ./o o Et------------·--·---o-. ··------ -- o-
+2o o-/ 0 0 o_o __ o __ Q _ _ _ _ ____ --o-u-- _ _a_ __ :X
--·----0 --- ·-··· ·--e---·---·--- -2o
0 5 10 DAYS
FIGURE 7 TYPICAL ANGULAR MEASUREMENTS
CJ) J::'
C)
o:l r )> (")
~ £Tl r ["
0
"'0 0 ::E
)> z 0
3:
;><: m )> (/)
-i
SLOPE MONITORING AT BRENDA MINE 65
pressure correction at the instrument only.
Readings are taken from one main station to monitor
ing points and the main backsite. As all main stations are
surveyed regularly. they can be considered stable. Any
error in backsite slope distance is applied to all other
distances measured from that particular set up.
Atmospheric corrections are proportional to the
measured distance. and the instrument error can be con
sidered to be constant for a particular set up.
The application of the correction could be made on a
distance proportional basis or as a constant if all dis-
tances are of the same order. Limited experiments did not
prove the "distance proportional" correction to be any
better than the constant. so the simpler constant method
was adopted. To obtain the best results it would be
advisable to use a backsight distance approximately equal
to the target distance.
The improvement in using this method is shown in
Figure 8.
3.3 Forced Centering With a Reference Reflector
A procedure recommended by AGA8.
The instrument uses three frequencies to resolve the
en en
540.06 - ,.. .D. Reading Taken
...../ ~
\ !::& .D. A -- Normalized
540.04 -G'l -Ctl r
SLOPE \ )> (')
~ rn
540.02 - \.. r ["
0
DISTANCE
\ -.,
Blast in 0 ~
540.00 - vicinity of )> z
~ 0
(Metres) station 3:
;;o;: rn )>
539.98 ~ ~ £::::.. (J>
-i
lo Is llo DAYS
FIGURE 8 SLOPE DISTANCE NORMALIZED TO BACKSIGHT
SLOPE MONITORING AT BRENDA MINE 67
target distance. The final 5 metre resolution utilizes a
10 metre wave length. The phase difference does not acc
ount for negative or positive par ts of the wave form. The
effect ive range of this final wave form is 10/2 or 5 metre.
Errors in the wave form would be eliminated if read
ings to a known backsight used the same part of the wave
form.
If readings were taken quickly from monitor to ref
erence to monitor etc., etc., the drift in readings would
cease to have a great effect, and other internal machine
errors would be reduced.
The only problems remaining are atmospheric correct
ions. If the reference and monitor are at the same dis
tance and in the same area, then the atmospheric correction
need not be considered. The computation of the monitor
distance will always be corrected regardless of what is
dialed into the machine.
It is more convenient to use a short reference
distance . In this case the atmospheric correction is not
dialed in, but computed and added to the final resul t late~
Only the distance to the monitor is found using all three
frequencies. From this point on, the machine is left in
the 10 metre wavelength, and only the las t two dig its
change for each reading. An example of the calculations
68 G. BLACKWELL) D. POW AND M. KEAST
required i s g i ven in Tab l e 2 .
The data plotted in Figure 9, shows tha~ !z mm can be
obtained without much effort . We feel that night su rveys
with great attention paid to setting of reference re flector
and atmospheric data could reduce this to ±1 mm. The
method is a little tedious , but would have an application
where a f ine degree of accuracy was required.
3 .4 Usi ng Inexpensive Pl astic Reflectors
To adequately monitor a pit slope, a reflec tor would
be required for about 50,000 square feet of face. A pit
one mile wide would need about ZOO reflectors. Problem
areas would use as many again.
The variation in cost of using $2 p l astic or $50
glass reflectors is $800 to $20,000. The best system would
usc mainly plastic reflectors.
Unfortunately the range of these units is not suff
icient for sighting across an open pit. The ins trument
must then be brought close to the reflector.
I n an operating pi t a temporary station is not t he
ans wer . A method mus t be established to accurately find
any i nstrument position and transfer this to the target.
As benches are mined, the ins trument position changes.
SLOPE MONITORING AT BRENDA MINE 69
TABLE 2
Tabulation of Forced Reference Method
SLOPE DISTANCE
FACE LEFT FACE RIGHT Station Reference Station Reference
676.099 89 96 96 97
676.092 676.096 676.091 85 93 86 88 90 83 86 89 88 92 96 85
676.0954 676.0886 676.0928 676.0866
Mean Station Reference
676.0941 676.0876 (16. 08 76)
As only frequency (2) used, readings to reference station are 676. Actual distance is 16.
Mean Temp. 49°F Pressure 24.73 ins
Correction Factor 68.5 (AGA Table)
Corrections
Stat i on ~ 676.0941 X 68.5 X 10· 6 0.0463
Reference + 16.0876 x 68.5 x 10- 6 : 0.0011
Corrected for Atmospheric Effects
Station
Reference
676.0941 + 0.0463
16.0876 + 0.0011
676.1404
16.0887
But the reference station distance is 16.0900
Correction ~ 16.0900 - 16.0887 = + 0.0013
Station Distance = 676.1404 + 0.0013 = 676.1417
70 G. BLACKWELL, D. POW AND M. KEAST
676.10 0
Values of
Station 0 & (J
before any 0 0 0.006
corrections 0 676.08 0 0
+ + ++ 70 + +
Thumb\vhee1 ++ correction
65 --+
676.15 -Station after D atmospher{f]
D cP 0 0.005
corrections 0 676.13 0 0 16.095
Reference~ ~ A .6. A
A target 0.005
16.07 5 A A
676.150-Corrected • • • • 0.002 676.140 -· • • • •
10 I
110 DAYS
FIGURE 9 USE OF A FORCED REFERENCE REFLECTOR
SLOPE MONITORING AT BRENDA MINE 71
Step one is to sight as many main stations around the
pit as possible and use all the information to give a mean
instrument position. As hoth angles and distances are
measured, combinations of triangulation and trilateration
can be used. The numher of calculations and solutions are
such that a computer program was written for the purpose.
A triangle comprising two main and one instrument
station has two cosine rule and up to eight sine rule
solutions for latitude and departure. Further main
stations increase the solutions factorjally. F.levations
are simpler.
Instrument positions found from three stations
generally have a spread of 3 to 10 mm in latitude and
departure. Elevations have about half the spread. Errors
in the system include computer error (~2 mm), atmospheric
conditions (!2 mm). The mean co-ordinates are probably in
the ts n~ range.
Transferring the co-ordinates from instrument to
plastic reflector is quite simple.
As with every other system, an excessive amount of
data is collected at the start. Presently four sightings
are made onto all stations, using 0° and 90° quadrants.
Readings are read into a tape recorder and cards punched
directly. Eventually we hope to decrease the sightings
72 G. BLACKWELL~ D. POW AND M, KEAST
to two per station on one quadrant only. Figure 10 shows
typical data. As movement is known to be occurring in this
area, the standard deviations arc high.
A series of ten set ups would probably find a move
ment of 5-10 mm in any direction. At present a set up
takes about 2 hours including keypunching cards.
The system is also useful in monitoring the main
stations. Any movement of a main station affects the
instrument co-ordinates. Experiments have shown that the
moving main station can be easily isolated from the data.
4. A CASE HISTORY
The south wall at Brenda has two main jointing
patterns. Analysed by photogrammetric methods these are:
a) strike 085/265 "±25°, dip 45° North ±so
b) strike 075/255 ~10°, dip 72° South :!: 50
The 45° dipping pattern is not continuous.
A study was undertaken to find the mechanical proper
ties of the 45° North dipping set. A Hoek shear box was
used for this purpose. Normal loads of 0 - 350 psi and
shear of 0 - 250 were used. Cohesion intercept values
varied between 0 and 20 psi, and friction angles of 25° -
35° found. A vertical hole was drilled to check water
levels in the area.
0 v 2140.78 0 va lue Lat itude 0 0.009 (met e rs) 0 21 40 . 76 0 0 (/)
r 0 ·-o
318 0.52 m
0 3: Departure 0 0
:z -(meters )
0 . 011
-1 0 ;o -3180 . 50 0 0 ~
D D > -1
5142.69 b. OJ
b. b. ;:u
El evation m .6. :z
b. o.oo s 0 ~
(meter s ) b. ::;: -5142 . 67 :z
m
0 s DAYS
FIGURE 10 LATITUDE, DEPARTURE AND ELEVATION OF PLASTIC REFLECTOR FROM TEMPORARY STATIO~ ""'-.!
\..N
74 G, BLACK~IELL~ D, POW AND M, KEAST
A basic analysis was carried out using methods given
by Hoek9. This showed the area to be very stable when ury.
A high water table decreased the stabilities. A plane
failure on the 45° joint system was assumed with tension
cracks formed on the 72° plane.
The south wall area is shown in Figure 11. Stabil·
ization of the area was not carried out, as the cost and
time spent was not warranted. The haul road will not be
used after Pit (1) is completed this year (1975). Further
it would be possible to reroute traffic through Pit 3.
There are three main causes of instability in this
case.
a) Natural jointing patterns.
b) Water pressure.
c) Blasting shocks.
The natural jointing pattern causes the bench face to
break as a series of steps. The failure mode would be a
combination of toppling and plane failure. Cable bolting
would strengthen both planes, and has been \~ell documcnted1 ~
Water pressure \~ould be a problem in spring, when pit pump
ing volumes increase from the normal 0 - 100 gal/min to up
to 2000 gal/min for a few weeks. Theoretically, any weak
ness in the area would have appeared at this time.
SLOPE MONITORING AT BRENDA MINE 75
Any slope dewatering system would have to be designed
for the spring peak, and consequently this might not provo
feasible with gravity flow from boreholes.
The effects of blasting in the area eventually caused
a small movement on a 'nose ' on the south wall. Cracks
appeared on the haul road. A more complete monitoring
system was then installed to show the extent of the move-
ment. Figure 12 shows the movement to date.
With water in the water monitoring borehole slowly
dropping, the area should become more stable. Blasting
immediately below the area and the resulting movement are
shown for one station in Figure 13. The slope distances
were measured from a station oblique to the movement.
Despite this, the advantages of measuring distances rather
that angles can be seen.
Some measure of stability would be attained by
decreasing blast pattern sizes or increasing the number of
delays used. This would uecrease the scaled distance
(distance from blast /we ight of explosive112) and decrease
vibration11 .
The sinking cuts necessary to take out the next level
gave o;wl/2 of about 3-4 ft/lbl/2 in the failing area. The
relation between blasting and movement confirmed that the
post shear trim blasting technique now in use for three
' Plan Scale
~- -- l~g~
........._
----Metres Feet
I / "' - '- 0 """ f-0 ------
_____ 14.J Metre 0.4 Feet
~ovement
'-..... Vector Scale 1\:--!orth - ------- .....__
-........._-"--..... ---~ L ~ ;z ._____
/
G 25
i
------ -- --- -- -Crest: ----- I
Direction and Magnitude of Hori~ont:al Movement -f -~- .......... "" AI
"""' /' .. ,-.._---4>-.-. 24
-.........._, :17 '--v
' I I ---......
I HAUL ROAD
.
d 23
v~ .... ,
--""-..-., ........._
<!:' 22
r- - ::::'"' ~--
.___ ______ --..... ___
Actual Movement Described by Horizontal and Vertical Vectors
.....__
~ SKETCH OF MONITORED
~ AREA
FIGURE 12
----.--
__/
121 1:;7
,---........ ,
---
" en
G'l
to
~ ("')
2 m r ["
t:'
"'tt
~ > ::z '=' 3:
"' m > en -1
-09° 24' 00_"_
Vertical
Angle
-09°24 I 40_"_
65°00'40"
Horizontal
65°00'00"
Angle
64°59'20"
--. -.. -"'-.
"'-. "'-. C'l
~ t:t:l 0 0 ...... '3:
-............_ tTl o-i tTl :;d
1;0 ::0 m :;... ~ 0 0 ::0: z 'll 0 ::0 --""'
. -- 0 _......--·-- > - ·- · >< en
ro 5
---,
/ /
\ \ -
Slope Distance (Metres)
Vertical Angle
Horizontal
-· - , .--- I ---
ill· 200
./ ./
/ 540.100 _, --
-·-------·~'-. t- - b:l b:l :;... -- t-~ "'---------- ~ ~ 540.000
en -~ -539.900
l1s l2o l25 l3o l3s DAYS
BLASTING EFFECT ON STABILITY
FIGURE 13
(I)
r 0 \) m
3
~ --1 0 ;:o -z C'l
)> -1
ttl ;:o m % 0 )>
3 ..... z m
"""-~ """-~
78 G. BLACKWELL, D. POW AND M. KEAST
years should be continued. (Loading 4 inch cardboard tubes
inserted in the 12 inch drill hoJes. Spacing is IS ft and
subgrade 3ft).
the area is now monitored using the plastic reflect
ors as in Section 3.4.
5. CONCLUSION
The EDM/1beodolite system is adequate for monitoring
known problem areas. It also has the abilities to detect
movements which apparently are of no immediate concern.
The calculation and display of data can be automated
using an electronic geodimeter with a punch tape recorder.
As a pit enlarges and workloads increase, manpower require
ments can be kept at a minimum.
The use of inexpensive plastic reflectors and poor
quality prisms would offset the high capital cost of the
system.
ACKNOWLEDGEMENTS
We wish to thank the management of Brenda Mines Ltd.
for permission to present this paper.
The assistance of the mine staff in the project was
appreciated. We are grateful for the help given by
Agatronics and many other geodetic instrument manufacturers.
SLOPE MONITORING AT BRENDA MINE 79
REfERENCES
1. Stability in Open Pit Mining; Proceedings of the First International Conference on Stability in Open Pit Mining, Vancouver, B.C., November 23-25, 1970. Brawne~ C.O. and Milligan, V., Editors, Society of Mining Engineers of A.I.M.E.
2 . Geotechnical Practice for Stability in Open Pit Mining; Proceedings of the Second International Conference on Stability in Open Pit Mining, Vancouver, B.C., November 1-2, 1971. Brawner, C.O. and Milligan, V., Editors, Society of Mining Engineers of A.I.M.E.
3. Geodimeter 710 Operating Manual; AGATRONICS LTD., 41 Horner Ave., Unit S, Toronto, Ont.
4 . Johansson, R.; Electronic Distance Measuring. Australian Electronics Engineering, April 22.
S. American National Standard for the Safe Use of Lasers, Z 136. 1-1973; American National Standards Institute, New York, U.S.A.
6. Winiherg, F.; Metalliferous Mine Surveying. Mining Publications Ltd., London, England, 1957.
7. Hedley, D.G.F.; Triangulation and Trilateration Methods of Measuring Slope Movement. D.E.M.R., Internal Report 72/69, Mines Branch, Ottawa, 1972.
8. AGA Geodimeter Model 6B; Publication 571. 1523. AGATRONICS, Toronto, Ont.
9 . Hoek, E and Bray, J.W.; Rock Slope Engineering. I.M.M. London, England 1974.
10. Seegmiller, B.L.; How Cable Bolt Stabilization May Benefit Open Pit Operations. Mining Engineering, December 1974.
11 . Bauer, A.; Open Pit Explosives Drilling and Blasting. Mining Engineering Dept., Queen's University, Kingston, Ont.
SUPER SCALE RESOURCE DEVELOPMENT
1 E. W. Brooker, P.Eng. 2 D. W. Devenny, P.Eng~ P. L. Hall, P.Geol.
1. INTRODUCTION
81
Large-scale resource development provides one of the
most challenging fields open to geotechnical or earth
science engineering.
The growing world demand for energy, water, and other
raw materials has resulted in accelerated exploitation of
1 President, EBA Engineer ing Consultants Ltd ., Edmonton
2 Senior Geote;hnical Engineer, EBA Engineering Consul tans Ltd., Edmonton
3 Senior Hydrogeologist, EBA Engineering Consultants Ltd ., Edmonton
82 E. BROOKERJ DJ DEVENNY AND P, HALL
the natural resources through what may be termed "super
scale" projects. The term "supcrscale" is applied to pro
j ects of the magnitude of Syncrude, the Arctic Gas pipe
lines, the James Bay project, and others of similar multi
billion dollar scope.
Because of the large scale of today's developments,
they have the potentia l of interacting with nature on a
scal e previously unknown to man . The speed with which these
proj ects arc initia ted may lead to adverse deve lopment
featur es before the effects on environment or project
operat i ons can be recognized. After inception, so much
funding will have been committed to the project that the
developer might be unable to stop or change direction.
With the advent of superscale projects, there is a
greater need for appreciation of natural site conditions.
Immediate and long term effects of natural condi tions on
t he project as well as the reverse effect must be consider
ed in all phases of development.
2. SUPERSCALE PROJECTS
A comparison of conventiona l and superscale projects
is considered in Figure 1. 1'/hereas there have been many
projects within Alherta and the Nor thwest Territories
SUPER SCALE RESOURCE DEVELOPMENT 83
PROJECT TYPE
CONVENTIONAL SUPE~ SCALE
SCOPE Small - $50-tOO Million Large - $1 Billion up - Gas Plants - Syncrude - Compressor Stations - Arctic gas, ell l ines - Commercial complexes -James Bay
IMPACT Local Vast - National & lnterna-tlonal
Not large Political Ralalively little disturbance Sociological
Economic Envi<enmental
MANAGEMENT & Close to problem & site Remote -National ENGINEERING Direct Communication International
Complex Communications Otten Third Party
REGULATION Open & Aexible Difficult to Assest Ready implementation & Modify
of Changes Inflexible Existing regulations Existing regulations may
workable be ineffective
APPRAISAL Open Obscure & Complex
INTERACTION OF PROJECT COMPONENTS Sli!lht extreme
FIG. 1 CONVENTIONAL vs SUPER SCALE PROJECTS
84 E. BROOKER~ D, DEVENNY AND P, HALL
involving the expenditure of up to one hundred million dol
lars, there is a recent trend to rapid development of multi
billion dollar projects. Within these projects, there are
profound differences in the range of impact on geological
and environmental conditions. Management and engineering
of such projects are also substantially different and the
regulation of the development poses new problems for govern
ment.
Superscale projects require well planned advance
studies and evaluation of all factors involved in the pro
ject. The economi cs of the development may be threatened
if this is not done.
The development of tarsand is an outstanding example
of the care with which superscale developments must be
treated. As demonstrated in Figure 2, tarsand is a unique
material affected by a variety of factors. There are sev
eral geotechnical fields which must be intense l y cons i dered
in tarsand development. These include geology, ground water,
materjal properties, climate, and other site resources.
Each of those areas interact and has an impact on the im
portant development components consisting of:
GEOTECHNICAL FIELDS TARSAND IN TARSAND DEVELOPMENT
A UNIQUE MATERIAL
AFFECTED BY ~ GEOLOGY VARIABLE $OILS
I STRATIGRAPHY
TRAFFIC STRUCTURE Joints
' TEMPERATURE F.:tults PROCESSING - FROST S1nkholes
li1hQI09)'
GROUND WATER SUR~ICIAL INTERMEDIATE DEPTH
I O~EP SALINE WATEA ,.... ,.... ,.... ,.... COLLI;CTION DISPOSAL REGIONAL CONSIDERATION$ EXt$TING DRAINAGE
~ I CLIMATE RESIDUAL STRESSES MINING PROCEDURE SE.ASON.._L TEMPERATURE
PRECIPil AT ION FROST ACTION
SITE RESOURCES CONSTRUCTION MATEAIALS WASTE MATERIALS (Mu$k<g)
FIG. 2 FACTS OF SrTE GEOTECHNOLOGY
IMPACTS
ON
I MINE SLOPES WATER WATER DISPOSAL MINING METHOD
PLANT STORAGE EXTRACTION UPGRADING
WASTE TAILING$ WATER
STORAGE TANK$ BITUMEN SULPHUR COKE
RECLAMATION
t/)
c: '"0 m ~
(/) ("') )> r rn ::tJ m (F) 0 c: ::tJ ("') m
0 m < m r 0 '"0 ::;:: m z -l
Q:) U"l
86 E·, BROOKERJ D, DEVENNY AND P, HALL
1. the mine,
2. the plant site,
3. waste disposal,
4. product storage, and
s. site reclamation.
The management of this complex relationship provides
a significant challenge to the areas of engineering, indus
try, and government.
3. SHORTCOMINGS OF THE PRESENT DEVELOPMENT FORMAT
Superscale development of natural resources in Alberta
is in early formative stages; as a result, there is a gen
eral lack of experience or guidelines for developers, the
engineering profession, and government to follow. It is
desireable that an approach to project evaluatio~ be devel
oped which provides the most effective and economical solu
tion.
Although geotechnical and ground water considerations
are among the primary facto rs controlling development of
large leases, the application of appropriate expertise to
provide baseline information, and effective evaluation of
that information, is occasionally overlooked.
SUPER SCALE RESOURCE DEVELOPMENT 87
In considering the nature of the baseline information,
it is important to delineate the significant factors in
quantitative terminology. Whereas the implications of this
aspect of development are of limited impact in conventional
projects, the problem may be profound in superscale projects
as indicated in Figure 1.
4. SIGNIFICANCE OF DEVELOPMENT APPROACH
Concerns relating to development format manifest them
selves in a dominant fashion in the field of earth science
engineering. As outlined in Figure 2, the various natural
conditions will have an impact on each element of the pro
ject and vice versa. The excavation.of a large scale open
pit mine may alter the regional ground water pattern to a
significant degree. This alteration may be further compoun
ded by the development of vast tailing retention areas.
Failure to optimize both mining and tailing disposal devel
opment elements will result in a less than optimum economic
development.
It is the goal of industry to extract resources with
a minimum of expenditure. This is most likely to be accom
plished if mining, plant, and waste disposal schemes are
selected which interact most favourably with natural
conditions. Failure to recognize and work with natural
88 E, BROOKER, D, DEVENNY AND P, HALL
conditions may give rise to adverse circumstance in the
planning and execution of:
1 . m inc layout,
2 . plnnt location,
3 . excavation equipment, and
4 . waste disposal (method anJ location).
The optimum size, orjentation, and depth of a mine
will depend on the natural conditions present on site and
on the equipment selected to mine the ore. If the site is
highly structured, its effect becomes more signiricant and
mining operations will work with or against nature depending
on the layout selected. Mining operations are expensive and
therefore, recognition of the above interacting factors is
important if optimization is to be achieved.
Optimum selection of mine e4ulpment is a funct ion of
tarsand properties, stable slope configuration, conditions
in the mine, layout required for optimum performance of that
e4uipment, and finally the efficiency of the equipment it
self. Appreciation of these interactions is important
because equipment costs are significant on superscale pro
jects and lead times to secure u replacement of unique equip
ment are long.
SUPER SCALE RESOURCE DEVELOPMENT 89
Excavation of the Atha basca tarsands will inter~ept
aquifers at various elevations . The pressures and quanti
ties of water involved arc criti~al l y important to s l ope
stability and mine pit conditions. There are areas where
extens ive depres s ur ization o f the aquifers is nece ssary
before mining can ta ke pJace. Consistent with this depres
surization is the need to dispose o f substanti al quant i ties
of water that may be saline. The approp ria te method of
handling this water involves an evaluat ion of both local and
regional hydrogeological conditions.
Large waste disposal areas must be developed to accom
modate the large quantities of tailings which are produ~ ed
hy tarsand processing. The develo pment of these tailings
ponds has an impact on local hydrogeological condit ions
which must he evaluated. The fai lure of a disposal area has
the potential of discha rging si l ts and sl udges which may
ultima tely pollut e t he entire downstream drainage system.
This could have far reaching effects since the tai lings arc
i nherently toxic. Notwi thstanding the environmental aspect
of a dam or mine pit slope failure, there is the criti~al
considera tion of project economy. Either failure cou ld re
sult in p lant shut down with losses measure~ in multiples
of millions of dollars. This aspe~t has a n effe c t on the
economy of the proje<.: t itselr a nd on the s urrounding ~ orn~~tun
ity. It is desir cable, the refore , that u systemat ic unJ
90 E, BROOKERi D. DEVENNY AND P. HALL
effective method of appraising project components to be
implemented.
5. A METHOD OF APPRAISAL
An appropriate method of appraising geotechnical and
environmental circumstances must consider all aspects of
project development. The following suggested methods apply
to superscale projects.
Secondary aspects, although still important, include
indirect changes in the biosphere. These changes can only
be predicted after the physical environment is understood.
The evaluation process, which of necessity is multi
disciplinary in nature, should encompass all natural condi
tions and planned activities. The purpose is to appraise
the effec t of each factor on the site development and to
adjust the development so that an optimum relationship
exists.
All areas should be investigated bearing in mind the
ultimate goal of reclama tion.
MINING OPERATIONS MAY CAUSE CHANGES IN GROUND WATER FLOW
EXAMPLE:
MINING OPERATIONS IN THE TAASANOS CAUSE CHANGES IN THE REGIONAL GAOUNO WATER FLOW PATTERN. TliESE CHANGES MAY RESULT IN SECONDARY EFFECTS ON SURFACE WA"Tl:A FlOW AND VEGETATION
-------LJ..,~ '-"''(hC'fOIIIII ~ Q~E .... 'II.'"'KTI(IIol
l:j 'wo •·~~ov •wlr•u,cr•ow
IN TURN, THIS CHANGE MAY CAUSE SECONDARY EFFECTS IN OTHER
SECTORS Of THE ENVIRONMENT.
FIG.3 INTERACTION APPRAISAL
(/)
c
" m ":x:J
(/)
0 ):> r m
::0 m (/)
0 c ::0 0 m
0 rn < m r 0 -o 3 m :z -t
1..0 .........
92 E, BROOKER, D. DEVENNY AND P , HALL
6. TilE OBSERVATIONAL APPROAC!l
Early this century, one of the most outstanding c ivil
engineers, Dr. Karl Tcrzaghi, evolved what is now referred
to as "the Observational Approach". This approach \~as orig
inally designated by Terzaghi as pertinent to geotechnical
matters. 1t is equally applicable to environmental matters
and to large scale natural resource development. Detai ls
are outlined in Figure 4.
The observational approach involves formulation of an
initial project concept on the basis of experience and
judgement. Work proceeds on this basis, bu t research is
initiated to explore areas of uncertainty (laboratory test
ing, analysis, and field explorat ion) and development pro
ceeds under close observation. As information and experi
ence develop, the initial concepts can be reappraised and
design modifications made as necessary.
The observational approach is an ite rative one that
permits optimum development. It is superior to method s that
attempt to cover every aspect of development in detail
before start up but that have no mechanism to ohserve and
learn from operations in progress. The most effective area
in which to apply this technique is in the field of the
earth sciences, where a total understanding of site condi -
SUPER SCALE RESOURCE DEVELOPMENT 93
I INITIAL CONCEPT l ' EXF>ERIENCE
JUDGEMENT WORKING HYPOTHESIS
' + ANALYSIS TESTING Geology Field
Hydrology Laboratory Soil Mechanics Geotechnical Rock Mechanics Hydrologic
I I
' ACTUAL OPERATION EXPERIENCE
DESIGN MODIFICATION
FIG. 4 OBSERVATIONAL APPROACH
94 E. BROOKER, D, DEVENNY AND P, HALL
tions or interaction is never possible. Major resource
development falls within this category.
Collection and interpretation of pertinent baseline
data is the first step. The initial data need not be all
inclusive but only sufficient to support or lay the basis
for amendment of the initial project concept. Part of the
underlying philosophy in implementing the observational
approach is the development of a working hypothesis does not
require design for worst possible ~onditions provided the
flexibility of recycling information into the stream of
experience and judgement remains possible.
One o[ the potential downfalls in the management of
superscalc projects is that this flexibility may not exist .
Plexibility must be present if the project is to benefit
from the observational approach.
7. COORDINATION OF fFrORTS
ln order to achieve full benefit of the observational
appoTach, it is necessary that three primary conditions pre
vail. These conditions are:
l. functional coordination of all developmeJit aspects,
SUPER SCALE RESOURCE DEVELOPMENT 95
2 . the interaction of engineering efforts with the deve1-
opment industry and government agencies, and
3 . continuity of effort from planning through construc
tion and operation.
The functional coordination of civil engineering as
pects is shown diagramatically in Figure 5. All phases of
site development should be suhjected to similar scrutiny if
impacts are to be fuJly appreciated and effective optimiza
tion with nature achieved.
The interaction of the engineering, industry, and
government functions is demonstrated in figure 6. An open
relationship must exist between these bodies in order to
optimize the proposed development. The tasks of each seg
ment are shown. Some areas of industry tacitly include an
engineering function as well. It is this latter area which
has led to the implementation of secrecy. However, with the
exception of highly specialized and patentable processing
techniques, it is suggested that secrecy in ~egard to geo
technical and environmental matters which impact on a re
gional basis is inappropriate. The functional coordination
as demonstrated in rigure S is oriented dominantly to geo
technical and earth sciences areas.
Site ~ Ot..,..S()r>mtnt Plant
11 Min• E$fA$4.1$K
Tt~!ii\QI• FUHCTIONH.. A£\l'll.WWI'TH REQUIREMENTS TOTAL P\.AN1 ....... . COHS!Of RAT IONS
CONC:ifl"' Wlfi<IIN Q£0TtCI<INJC;At. ,.-
r±; QUIOEL*IES RiYIEW OESIQH WrTH REFtltENCE 10$rTE
~ eOICIT'!OtlS
..... ACPOAf
RE'V\.f:W TOTAL
~ fM\IlltONMf!nAL IIAPA(;f
IOiNTIFY OftlON ~1A AI::OlJIAI::D &Y QEOTECMNICAl CONSUI.T'NTS
~r OOORM-!AT£ OfOT6CHHlCM • ._,'E~r•QATION ....... «<NISoVLY/oHf
FIG. 5 FUNCTIONAL COORDINATION
CONYil'IIUCliO!f
nltor
~uirod
<..0 0"'1
m
., ~ 0 0 :A m ~
" 0
0 m < m z :z -< )> z 0
""0
:I: )> r r
SUPER SCALE RESOURCE DEVELOPMEi'H
ENGINEER Apl)r~ise Site Conditions
Predict Development Interaction Recommend & Lay Out Reg. Studies
Execute Effective Studies Carry Out Effective Monitoring
Recognize Deviations from Expectations and Correct
GOVERNMENT Regvlatory
Environmental Protection Review Permits
Assess Fe~s<bility Coord in ate Activities
INDUSTRY Optimize Development
Economic AJ;>I)raisat Effective Operation
Monitor ..... -----~------'
FIG. 6 DEVELOPMENT INTERACTION
97
98 E, BROOKER1 D, DEVENNY AND P, HALL
figures 4, 5 and 6 demonstrate that an interaction and
iterative pro~edure is necessary in order to achieve the
desired goals and this can only be achieved by the coopera
tive use of multidisciplinary teams. The need for contin
uity in the review process is obvious.
The function of government within the areas of devel
opment deserves special mention. Regulations on environ
mental protection are a natural function. Less obvious is
the granting of permits, which is necessary because of the
massive socio-economic impacts of these superscale projects.
Continual monitoring of the environment and reassessment of
development assumptions should also be carried out in close
cooperation with government agen~ies.
8. RECOMMENDATIONS
The foregoing text suggests that the relationship
between project development and natural environmental con
ditions must be effectively integrated on a logical basis in
order to provide optimum development. The relationships
have been shown and a method has been outlined for achieving
this desirable goal.
Emphasis has been placed on the collection of rational
baseline data necessary for appraisal leading to optimum
SUPER SCALE RESOURCE DEVEL0Pji1ENT 99
development. The foregoing suggestions relate primarily to
superscale projects which differ significantly from conven
tional projects. The significant features related to super
scale projects are illustrated in Figure 1. Useful con
clusions may be drawn from this figure in regard to neces
sary engineering activities. The following recommendations
are suggested in order to optimize development of our
natural resources.
1 . A policy of recognizing and working with natural con
ditions can provide the basis for selecting optimum
development schemes and should be implemented.
2 . Appropriate studies to identify and appraise these
natural conditions should be carried out prior to,
during, and subsequent to development.
3 . There should be effective coordination and integra
tion of various site studies.
4 . Project development should include design that recog
nizes environmental protection, reclamation and long
term geotechnical effects.
s. Optimum use of Canadian professional capability should
be encouraged and integrated to its maximum extent
100 E, BROOKERJ D, DEVENNY AND P, HALL
so that our human resources may grow as our natural
resources decline.
6 . Licensing agencies should issue guidelines for proper
deve lopment, review applications, and then mon itor
work in progress. Submissions for development should
be reviewed on an economic basis and also on a tech
nical basis tha t considers pertinent geotechnica l and
environmental factors. Several public hearings would
be required to accomplish this.
7 . The government and its various regulatory agencies
shou l d encourage coordinated cooperative studies of
resou rce potential and development proposals. In·
formation obtained could be used to monitor projects
underway and also appl ied to future developments.
8 . The observat ional method of approaching geotechnical
and related environmental problems should be an under
lyi ng worki ng philosophy in all developments which
rela te to the rearrangement of natural condit ions .
I t is concl uded that no other development area is
more amenable to the foregoing procedure than the exploita
tion o f t he Athabasca tarsands. The unique nature of this
SUPER SCALE RESOURCE DEVELOPMENT 101
development requires a unique approach to deal with the
problems. The approach recommended is a coordinated obser
vational approach carried out by multidisciplinary teams.
The major challenge to the engineering profession at
this time is the implementation of rational procedures which
permit safe economical resource exploitation involving
mining, extraction, waste disposal, and reclamation on a
scale unique in the world. Major contributions to overall
project development can be achieved by utilizing the organ
ized philosophy of the observational approach which has been
used in the field of geotechnical engineering for a number
of years. Indeed, it is questionable if rational and
economical projects can be accomplished without implementa
tion of this process.
103
~10NITORING OF THE HOGARTH PIT HIGHWALL STEEP ROCK MINE
ATIKOKA~L ONTARIO
Abstract
C. 0. Brawner1
2 P. F. Stacey
R. Stark3
The development of unstable conditions in the Hogarth Pit hlghwall at Steep Rock is <Jescribed. The basis for the Company's decision to continue mining after institution of a detailed monitoring system is reviewed. The monitoring system included both triangulation and Electronic Distance Measuring surveying, extensometcrs, movement pins and seismograph and a visual guard. Mining operations were restri~ted to daylight hours and were revised to give the pit crews maximum protection.
Movements are Jescribed and the operational characteristics of each of the monitoring system elements are discussed.
1President, Golder Brawner & Asso~iates Ltd., Vancouver, B.C.
2senior Engineer, Golder Brawner~ Associates Ltd., Vancouver, B.C.
3senior Mining Engineer, Steep Rock Iron Mines Ltd., Atikokan, Ontario (Part A was prepared hy C. 0. Brawner and P. F. Stacey and Part B by R. Stark).
104 C, BRAWNERi P, STACEY AND R. STARK
Mining was completed in March 1975, with more ore than anticipated being recovered.
In early May, movements started to accelerate, and the major failure occurred in the predicted toppling mode.
Finally, the paper describes the program from the Mining aspect. Reasons for choosing a monitoring approach are given, and the effects of the revised mining procedures discussed. The Company policy of continual communication with its employees played a big part in the success of the program, and the choice of pit crew members to form the visual guards had several advantages.
MONITORING OF THE HOGARTH PIT HIGHWALL 105
PART A - GEOTECHNICAL ASPECTS
INTRODUCTI ON
This paper describes th e monitor ing program
developed to study movements in the highwa ll of t he llogarth
No . 1 Zone of Steep Rock Mi ne at Atikokan, Ontar i.o. As
such, it forms a case history of a successful mon i toring
program wh ich permi t ted removal of the recoverab l e ore
reserves from t hat ar ea of the mine, whi l e at the s ame time
provid i ng a cont ro l safe t y f or t he ope r ating cr ews .
The paper describes a case his tory of success ful
cooperation between a mining company and a consu l t ant. This
s uccess was enhanced by t he effective communication between
the Company and its employees , and the us e, where possible
of all l evels of Company personnel in the program .
I t must be stressed t ha t t he aim t hr oughout was t o
provide a pract i ca l solution to the p r actica l problem of
the safe ty of the min e crews .
HOGARTII NO . 1 ZONE
The Steep Rock ore zone is composed of a goethitic,
soft iron ore horizon, which di ps steeply to the west , and
is over l ain by a s h rock, and underlain by pain t r ock and
carbona t e . The t otal Steep Rock Compl ex is divided by
regional faults into t hree ma jor sections , each of which
originally outcropped unde r an arm of the Steep Rock Lake .
106 C, BRAWNER; P, STACEY AND R, STARK
The section of the orebody currently mined by
Steep Rock Iron Mines Ltd. is termed the Middle Arm Ore
body, referring to its respective arm of the lake. This
orebody is separated into several sections by faulting and
folding. The major divisions from south to north are
termed the Errington Zone, the Roberts Zone, and the Hogarth
Zone. At the north end of the Hogarth Zone the ore ter
minates against the Bartley Fault, which strikes northeast
southwest and dips to the southeast at 85°. Northwest of
the fault the original lakeshore was formed by a steep 300
ft. high wall comprised of a hornblende-biotite metadiorite.
The diorite contains sheared basic dykes which
parallel the Fault. It also contains two well developed
vertical joint sets which strike respectively parallel to
and perpendicular to the major fault direction. It was
these joint sets which controlled the development of the
pre-mining lakeshore, and which also controlled the failure
to be described. The entire failure was restricted to the
diorite highwall, although the monitoring program covered
the possibility of the onset of failure in the iron for
mation below.
The crest of the pit in the area of movement was
covered by loose blocks from the excavation of a cut for
the railway line to the pellet plant. This line runs
approximately 150 ft. behind the movement area. The loose
blocks caused initial problems in locating cracks, and sub-
MON IT JR I NG OF THE HOGARTH PIT HI GHWALL 107
~equently added to the diffjculty of traversing the area.
A plan of the Hogarth No. 1 Zone is shown in Figure
1 and an air photo of the highwall is shown in Figure 2.
ONSET OF foAILURE
A crack behind the crest of the diorite highwall
was first noticed in October 1973 and became the subject
of weekly observation. ~urthcr signs or instability
developed in April, 1974 when an attempt was made to access
the foot of the diorite wall at the 975 level on a berm
containing the Bartley rault outcrop. This level approxi
mates to the ore outcrop below the original lake floor.
A small blast on the hangingwall side of the berm resulted
in the failure of a small wedge of diorite bounded by
vertical joints. Talu~ spilled over the ore hcrm and down
the iron formation face below.
As a result of the crack on the crest opening and
extending, the Company installed a simple monitoring pin
system, which was read on a daily basis.
In mid-August 1974 a second crack was noticed,
approximately 150 ft. behind the crest, when craters
appeared in the debris from the rock cut. At this point
the pin monitors were supplemented by triangulation
stations and three elementary wire extensometers con
structed of drill steel and clothes line. On August 20th,
movements increased after a period of heavy rain. At this
I "'
108 C, BRAWNER, P . STACEY AND R. STARK
~ 1
DIORIT E
I
FIGURE I
I / / " I
,
/ ,
/ ~
I
HOGARTH
PIT
SCHEMATI C PLAN OF HOGARTH UO. I ZONE
MONITORING OF THE HOGARTH PIT HIGHWAL L 109
point the advice of Golder Brawner & Associates was sought .
RDV I EW o:r ALTERNATIVES
It was apparent that a serious slope instability
situation was developing. Accordingly, a temporary halt
was called to mining operations in the No. 1 Zone while the
movements were reviewed. A 5 mph Slow Order was placed on
trains operat ing on the track behind the highwall.
Tho review indicated increasing movement i.nvolving
between 200,000 and 250,000 cu. yds. of diorite. The
safest procedure would have been to discontinue mi.ning in
the area . However, since the llogarth No. l Zone was the
only major short term source of ore, two alternatives which
would allow ore production were considered. Attempts could
be made to fail the slope by flooding the cracks, or
blasting, after which the ore could be mined following a
delay for clean-up of the debris; or a comprehensive moni
toring system could be installed to provide warning of
potential failure to the pit crews working beloN. The
former course carried with it the risk of only partial
failure, possibly resulting in a less stable slope which
would terminate all mining activities. The latter course
was felt to be a safe approach, since geologic evidence,
existing monitoring data and the author's past experience ,
Brawner (1968, 1970, 1970, 1971, 1974) indi cated a
"toppling" mode of movement would be expected which would
110 C, BRAWN ER, P, STACEY AND R. STARK
give nmpJe warning of failure in t he form of ravelling and
an increasing rate of movement. Th is, comb i ned with t he
requirement to maintain committed pel let shipments, influ-
enced the (ompany's decision.
To assess whether cleft water pressures may he con-
tributing to instabili ty a piezometer was installed in a
hole dri lled from behind the crest. This indicated no
water in the dior i te behind the toe at the 975 ft. level.
This hole remained ury untU the standpipe \,·as finally
sheared by movement along the back crack.
MONI TORING SYSTrM ----WIIcn the deci sion was made to go ahead with a mining
and monitoring approach, the moni toring system established
by Steep Rock staff was expanded to include seven further
p in monitors (Figure 3), seven further wire extensomet ers
mounted on tripods (Figure 4) rather than drill steels ,
and an increased number of tri angulation stations. The
1~ ire ex tcnsometers wer e tensioned with 110 lb. weights so
wind, contact with bushes, etc. would not influence readings .
The results of the monitoring of the 14 triangula -
tion stations indicated a "toppl ing" mode of fai lu.-e, tofith
essentially horizontnl movement of the crest townrJs the
east-no.-theast, and negligible movement at the diorite or
iron formation toes. Daily triangulation by the pi t survey
<.:rei'' was both slo"' and impractical as a long term program,
MONITORING OF THE HOGARTH PIT HIGHWALL
FIGURE 2 AERIAL PHOTOGRAPH OF HOGARTH N0.1 ZO NE HIGHWALLSEPTEMBER 1974 (The location of t he main cracks is indicated. The arrow shows the site of t he guard shack . )
FIGURE 3 'MEASURING PIN MONITOR ACROSS BACK CRACK
111
112 C, BRAWNER) p , STACEY AND R, STARK
·~
FIGURE 4 EXTENSOMETER TR IPOD WITH LIM IT SW ITCH
MONITORING OF THE HOGARTH PIT HIGHWALL 113
it was decided to usc a laser Electronic Distance Measuring
device (EDM) (Figure 5) shooting across the pit along the
approximate line of movement. It should be noted that even
if the line of sight is off line of the direction or move
ment by as much as 45° the scale of the time-movement
graph is only reduced by about 30 per cent and warning of
impending instability is still readily available. Initially
10 EDM reflector prisms were installed on the crest, on the
975 ft. berm and on the Iron Formation face. Figure 6
shows typical EDM data which confirmed the toppling
mechanism. This general system remained in operation until
completion of mining, with three further prisms being added
on tho 712 bench. The EDM monitoring was supplemented by
periodic triangular surveys to obtain 3-dimensional vectors
of: movement.
Beside the overall "remote" EDM - triangulation
monitoring system, movement of major individual blocks
within the mass was monitored on a daily basis by the
network of extensometers. Limit switches connected to a
warning system involving sirens and flashing lights wore
attac~ed to strategic lines, and a light on the tripod
indicated that power was on and that the switch had not
been operated.
At a later date, at the request of second opinion
consultants employed by the Ontario Department of Mines,
twelve extensometers equipped with limit switches and a
114 C~ BRAWNERJ P, STACEY AND R, STARK
FIGURE 5 ELECTRONIC DISTANCE MEASURING DEVICE (EOM.)
MONITORING OF THE HOGARTH PIT HIGHWALL 115
(t Railway
Ke J 0
1mm.
\
\
550 mm .
\ \ \ \
\
1000 mm .
Bartley Fau It
975 Level
Schematic Only
FI GURE 6 RELATIVE EDH MONITOR DISPLACEMENT SEPTEMBER TO DECEMBER 1975
116 C, BRAWNER, P, STACEY AND R, STARK
micro-sei smograph were added. Throughout the mining
operation the limit swi tches were set for a predetermined
movement and were adjusted da lly . Prior to the onset of
winter conditions this tolerance was 1/2 inch .
During the initial stages of the monitoring program
the movements on the two major cracks were monitored at
seven ind ividual points using a three pin system . However,
by mid-winter the movement at several points had made this
operation too dangerous to continue.
An extremely important element of the monitoring
system was a 24 hour visual guard by pit crew members. A
heated shack was installed on the 1050 bench of the hang
ingwall. Two guards per shift had a complete view of the
highwall as well as the warning lights and s irens. Radio
and visual contact was maintained with the crews working
in the pit below . This included an hourly radio check with
each drill and shovel in the area. All events noted by
the guards were recorded in a logbook which was initialled
daily by the Mine Superintendent and by the Golder Brawner
representative. Based on pas t experience it was envi sioned
that any major failure would be preceded by ravelling of
rock blocks too small to be detected by the monitoring
system, the guards were intended as the firs t line of
~~•nn ing to the pit crew:; .
The Kinemetrics VR-1/SS-1 seismograph system
requested by the Depar tment of Mines was installed in
MONITORING OF THE HOGARTH PIT HIGHWALL 117
December. The ~eismograph head was installed in the centre
of the failure area, and the remote drum recorder was
located in the guard shack.
The daily monitor reading and compilation were
performed by a Golder Brawner field J::ngineer, who reported
the results to the Stoep Rock Senior Engineer and to Van
couver by Telex. Movement plots were posted daily in the
Mine Dry Room.
In sununary, the total system installed covered all
levels of monitoring from the EDM direct measurement system
and triangulation vectorial system, through the extenso
meters, which monitored major blocks within the mass, down
to the visual watch for the failure of small pieces. Oper
ational characteristics of each of the monitoring systems
and the selection and psychological effect of the guards
arc discussed later.
MINING SEQUENCE
The monitoring system was complemented by a planned
mining sequence. At the toe of the Highwall a 40 ft. wide
berm with rock pile was left on the 712 level. This berm
was intended to catch only the initial ravelling since a
more desireable, wider berm would have greatly reduced ore
reserves in the Zone. Below the 750 level, overall slopes
in tho Iron formation \vere designed at 40° instead of the
usual 42-1/2".
118 C, BRAWNERJ P. STACEY AND R. STARK
Prior to the mining of each bench, a 100 ft. wide
slot ~~as drilled, blasted and mi ned along t he foot - or
hangingwall contact of the ore up to the proposed Highwall
too. At the same time a 100 ft. wide zone was drilled off
along the base of the Highwall, perpendicular to the slot.
The holes in the zone had a maximum loading of 1,200 lb.
of explosive per delay and were fired into the slot . This
approach was aimed at r educing the exposure of men and
machines by relieving any stress in the toe and/or initi
ating any unheralded failure while the operating equipment
'"a s sti ll well back from the llighwall. For want of a
better word the procedure was termed "De-stressing".
At the same time a "Green line" was defined 300 ft.
from the llighwa 11 toe on each bench. This line, \vhich was
indicated in the field, became highly revered by the mining
crews. It formed an inner boundary for all nighttime and
bad weather operations. f-urther, no operation s were per
mitted within the Green line for 48 hours after a de
stressing blast and for 12 hours a(ter a production blast.
It is interesting to note that when the slope failed,
l ittle, if any, material passed this line.
I t was recognized that time was an important fac
tor. Accordingly, a series of six high-powered lights
were installed to illuminate the entire face, thereby
providing conditions under which the initial dayti me
operations could be safely extended to a 24 hour basis.
MONITORING OF THE HOGARTH PIT HIGHWALL 119
This move was not accepted by the Union, and operations
were restricted to good visibility conditions during day
light.
MOVEMENTS IN TilE P!::IUOD SEPTEMBER - JANUARY
The "toppling" movement pattern established .in
early September continued until January 9th. Movement was
restricted to the diorite above the ore berm with the two
sets of vertical cracks opening up and propagating down
'"ards. A small "wedge" on the east side of the main mass
showed more rapid movement, and on several occasions loose
material was scaled from this area by Steep Rock scaling
The extensometer and EDt--1 data sho\ved that there
were periods of constant movement rates separated by
periods of more accelerated movement. The acceleration of
movement appeared to correlate with heavy rainfall, there
being a time lag in the order of 1 day. It is not certain
whether blasting a1so had a contributing effect.
The triangulation surveys showed an interesting
vectorial picture. The materia 1 bett•een the face and the
original "front" crack showed a hori.zontal:vertical move
ment ratio in excess of 3:1, with no appreciable movement
at the toe, indicating toppling of this block. The block
bet1"een the front and back cracks showed a horL:onlal :vur·
tical movement ratio of approximately 1:1, indicating an
120 C, BRAWNER, P, STACEY AND R, STARK
outward slumping behind the front block. Monitoring of
survey stations on the 975 Ore Berm and Iron Format ion face
below indicated no movement.
All major movement continued to bo on an east
northeasterly azimuth, i.e. in the general direction of the
EDM unit.
WINTER MONITORING
On January 9th prolonged sub-freezing winter con
ditions, commenced with a blizzard. These conditions
generally persisted until af ter March lOth when min ing was
completed.
The sub-freezing conditions required variations in
the monitoring techniques. Rapid temperature fluc tuations
from +30 °F to -20°f experienced over a few hours would
result in rapid contraction of the extensomete r wires by
as much as 7/8 inch, with resultant tripping of the alarm
system. The maximum daily permis sible movement on an ex
tcnsometcr limit switch was therefore increased to 1 inch
to accommodate this phenomenon.
During extreme ly cold conditions the EDM readings
across the pit were affected by the temperature gradients
deve loped in the air. As a result there could be a di f
ferenc e of 2 em. between a reading made in the early mor
ning, and one taken in the late afternoon, partjcularly on
still, clear days. This problem was overcome partially by
MONITORING OF THE HOGARTH PIT HIGHWALL 121
referencing measurements to a stable station on the crest
of the railway cut.
Blizz ards or poor visibil ity resulted in the tem
porary cessation of operations, while the onset of thawing
condit ions resulted in a mandatory withdrawa l behind the
"Green Line".
Snow made negotiation of the boulders and cracks on
top of the movement area a t r eacher ous operation. Accor
dingly the cross-crack pin measurements were halte~, and,
by the time the snow had melted, many of the cracks were
too wide to measure safely.
MOVEMENTS JANUARY - MARCH
Contemporaneously with the onset of permanent sub
freezing conditions major movement essentially ceased.
Failure was still restricted to the area ln front of the
original back crack, and the main mass was now divided into
a series of slabs by the ope ning of vertical fractures .
Although daily movement dectcctable by the exten
someters and EDM had ceased, and variations in the trian
gulation survey data were generally within the limits of
accuracy, there was evidence that the slope was sti ll
active. Part icularly in cold weather water vapour was
emitted from the major cracks. During the night shift when
no equipment was operat ing i n the zone, occasional small
signatures appeared on the seismograph trace. In the day·
122 C. BRAWNER, P , STACEY AND R, STARK
time however, seismic indications of this type were masked
by mine equipment signatures so that warning was not avail
able from the seismic instrumentation. This confirms the
experience of Kennedy (1972) on the practi cal limitations
of the seismic monitor ing technique.
Much of the movement in this period '"as restricted
to a slight opening of the forward cracks on the face, and
later to the occasional loosening of debris on the slope
hy freeze-thaw action.
COMPLET!ON OF MINING
The planned ul timate depth of the No. 1 Zone at the
600 level was roached in late February. With movement on
the Highwall negligible, and horizontal drain holes drilled
into the face indicating no water within 50 ft., ci<cular
arc ana l yses were performed on the Iron Formation to assess
the effect of taking an additional lift. The analyses
showed only a minor influence on the Factor of Safety.
Accordingly an additional 20 ft. bench was mined. At the
completion of this level there was just sufficient width
of ore exposed in the floor to make an additional 20 foot
deep scram or rob cut feasible.
With continuous monitoring the scram was drilled up
to the toe of the previous bench and fired in one blast
using a maximum loading of 1,200 lb/delay. An intensif ied
monitoring system involving daily triangulat ion of 4 criti-
f10NITORING OF THE HOGARTH PIT HIGHWALL 123
cal stations , twi ce daily extensometer reading s and three
daily EDM surveys was instituted, and, after a del ay of 48
hours during which no movement wa s detected, mining recom
menced.
It was planned to drill a series of exploration
holes from the flo or of the Hogarth Zone on the footwall
side; t he original plan to mi ne in at 40° slopes on al l
sides and double-bench on the way out for maximum ore re
covery lvas modified to inc lude double-benching on the
hangingwall and highwall faces only.
Min ing of the scram cut to the 560 level was com
ple ted on March lO th. In total , 970 , 000 tons of ore were
recovered from the Hogarth No. 1 Zone compared Nith an
original estima te of 933,000 tons, in spite of an ore loss
on the footwall side. Part of this gain was due to the
mining of the two additiona l 20 ft. benches.
MOVEMENTS MARCH - FAILURE
Two levels of highwal l monitoring were established
after completion of mining, one to cove r drilling in the
No. 1 Zone, and a s e cond l evel aimed at monitoring for
movements which could affect the safety of the railway.
Dril ling started immediately after completion of
mining opera tions, but shortly thereafter the onset of per
manent thawing conditions , with re sultan t ravel l ing and
smal l fai lures in the ash rock led to the temporary remova l
124 C, BRAWNERJ P, STACEY AND R, STARK
of the drill to a safer locat ion.
By early May week ly reading of the extensometers
and monthly triangulation of 12 se lected survey points by
Steep Rock personnel i ndica ted a marked increase in move
ment on the Highwall. This coincided with a heavy rainfall.
Increased activity was also noted on the seismograph. The
movement followed the original pattern, with the vertical
fractures openi ng from the top in a toppling mode, and the
back block slumping behind the front block.
On May 21st a slab from the front of the main mas s
of about a hundred cu.yds. termed the Maple Leaf after the
shape of its bounding c rack, failed. Most of the material
from this failure was contained on the 975 Ore Be r m, none
of it reaching the pit floor. This fai lure was preceded by
minor ravelling, and was followed by accele rating movement,
accompanied by increased seismic activity and constant
ra,elling particularly from the wedge area.
On June lOth the Wedge fa iled involving several hun
dred cu. yds., followed on June 11th by a further section
from the fron t of the main mass. By thi s time both the 975
Ore and the catch berm at the 712 level were choked with
debr is , and large amounts of material started to reach the
pit floor.
As movement continued both sets of joints opened to
divide the mass into a seri es of vertical columns. The
pattern still remained that the front columns topp led for-
MONITORING OF THE HOGARTH PIT HIGHWALL 125
wards, while the back columns ti pped forward and slumped.
Most of the extensometers and EDM targets were destroyed in
the period June lOth to 11th, but immediately prior to this
dat e extensometers and laser targe ts in the centre of the
mass were recording movement s in excess of 1 ft./day
(Figure 7). On June 23rd, 5 hours before failure , a trian
gulat ion point on the front of the old front crack was mea
sured to have had a cumulative movement of 30.5 fe et hori
zontally and 4.8 feet vertically since Augus t 1974.
Heavy rainfa l l on J une 20th induced reneweo heavy
activity , and by June 23rd the face was s howing signs of
major dis tress. The remaining mass wa s keyed in by a block
on the west side. This was seen to be cracking badly, and
ravelling was general over the who le face . At 9:00 p.m.
the back mass slumped, pushing out the front columns .
Finally at 9:15p.m. the remaining mater ial failed in three
portions commencing i n the east. The largest , westernmost
column , es timated at about 50,000 cu.yds. failed in a
typical toppling mode, whereas the remainder broke up and
ravelled. See Figure 8 f or failure sequence photos .
The resul ts during the fi nal days prior to fai lure
indicated that even if failure had occurred while the
mining operations were stil l in progres s, the monitoring
systems would have given ample warning. Thus , t he decision
to proceed with the mining under a cont rol led monitoring
system was justified . Also, the instrumentation installed
126 C, BRAWNER, P, STACEY AND R. STARK
FIGURE 7
HOGARTH No 1 ZONE 'J' Monitors (Except J 5 & J 7) Total Displacement History
MAXJMVM DAt'-'t' TUIP£ftATORE
FIGURE 7 HOGARTH NO. I ZONE - 'J' MONITORS (EXCEPT JS & J7) TOTAL DISPlACEMENT HISTORY
MONITORING OF THE HOGARTH PIT HIGHWALL 127
~ ~
~ N
E v ~ c
~ ~ ~
~ ~ c
---- c ~ ~ ~
0 ~ 4 ~
~ ~ ~
M N
w % ~ ~
w ~ ~ ~
~ ~
z
~
00
w ~ ~ ~
~
E E ~
0 ~ 0
~ ~
~ ~
u
128 C, BRAWN ERJ P , STACEY AND R, STAR K
during August proved totally adequate and the time de1ay
and mine shutdown period required for additional instrumen
tation installation proved to be unwarranted.
Fin ally, the choice of a 300 ft. Green line was up
held, since little, if any , material extended beyond the
marks remaining on the benches in the Iron rormation.
PART B - MINING ASPECTS
The dec ision to strip and mine the No. 1 Zone of
the Hogarth Pit was not made unti 1 August, 1973. An expan
sian into the No. 1 Zone was not included in the original
planning becaus e the stripping ratio was fairly high and
the ore zone was not as wel l explored as the other 3 zones
of the pit. ln addition, a hangingwal1 failure immediately
adjacent to the highwall had terminated mining fourteen
years previ ously, thereby making strippi ng much more dif
f i c.:ult.
However, because of a shortfall in net excavation
in 1972, the decision was made to strip and mine the area
as part of the Hogarth pit design . Stripping in the No. 1
Zone began in September, 1973.
A crack had been detected as early as October, 1973
along the north wall of t he No. 1 Zone, Hogarth Pit, out
side the planned pit limits. Movemen t along the crack was
not detected however, until April of 1974. Movement was
of a minor nature and was not expect ed to have any adverse
MONITORING OF THE HOGARTH PIT HIGHWALL 129
effects on the stripping and mining operation. In early
August, when the stripping programme was almost complete~
and the mining programme was just beginning, movement ac
celerated. The ore resulting from the mining programme was
required within two months to maintain a continual supply
of ore to the pellet plant. In achieving this goal, the
safety of men and equipment working in the area must be
assured.
Steep Rock Iron Mines personnel have had consider
able experience in dealing with wall stability problems,
mainly associated with the hangingwall ashrock and footwall
paint rock. However, because of inexperience in the
diorite, and the tight mining schedule at that time, the
decision was made to consult an engineering group who had
had experience in this type of stability problem. Golder
Brawner & Associates were approached because of their diver
sified mine stability experience and professional reputa
tion throughout the world.
Golder personnel suggested two ways of dealing
with the problem. These were:
a) to induce a failure, clean it up and resume mining,
and
b) to continue to mine, after instituting a detailed
monitoring system.
~·o methods of inducing failure were considered.
The first was to drill a series of diagonal holes under the
130 C, BRAWNER, P, STACEY AND R. STARK
area and blast them, thereby unloading the slope. The
second was to flood the cracks with water.
The system of drilling diagonal holes was not con
sidered practi~al under the circumstances. The holes would
be expensive to drill and considerable time would be re
quired to complete the programme. Of a greater importan~e
was the fact that the cracks were opening continuously, and
it would be extremely difficult, if not impossible, to com
plete the holes.
If the alternate method of flooding the area was
used, approximately one month would be required to remove
the failed material from the pit bottom. Costs over and
above the extra cost to remove the failed material would be
incurred in handling the large blocks of rock normally
associated with wall failure, and in cleaning up the water
afterwards.
If the failure did not occur when the area was
flooded, it Nas reasonable to assume that the wall would be
stable and would probably not fail for some time. However,
if only a partial failure occurred, the situation would be
worsened rather than solved.
Because of the unknown factors associated with
failure induction, and the assurance that advance warning
of any impending failure would be given, the decision was
made to monitor and mine. There were limitations on this
solution, as mining would be governed on the basis of
MONITORING OF THE HOGARTH PIT HIGHWALL 131
monitoring resu lts and dayl ight hours only. It was esti
mated that mining in this manner would still provide ade
qua te ore to assure us of a continua) supply of ore to the
pellet plant. Should movement increase and a failure
occur, it was anticipated that the clean -up could be ~um
plcted and mining resumed with little or no disruption in
the pellet plant operation.
The decision to monitor and mine was made on the
basis that it was the most reliable system which could be
adop ted to achieve a continual ore supply to the plant.
Considering the economics involved, the decision
was also the bes t alternative. The actual cost of mon i
toring the wall including a resident Golder repres entative
and two guards full time was $163,300.00. The breakdown
of this total is $23,700.00 for diamond drilling,
$63,300.00 for consultant fees and $76,300.00 for operating
costs including the cost of monitor installations, guards,
etc . This cost \~as \<fell below the estimated cost of the
other alternatives.
RESTRICTION OF MI NING SEQUENCE
The mining sequence as recommended by Golder
Brawner had some adverse affects on the mining programme in
one zone.
First of all, the slot type approach limited us to
one shovel earlier in the programme than we had anticipated.
132 C. BRAWNER~ P, STACEY AND R, STARK
Because of the confined area, a t1vo shovel ope ration \vas
not very effective under normal circumstances . With the
slot type approach it eliminated any chance to operate two
shovels effectively.
The destressing blast limit of 1,200 lhs. per delay
necessitated in a very low powder factor for the material
against the wall. As a result, the material was not well
broken and tough digging conditions were experienced.
The 48 hour waiting per iod after the destressing
blast delayed the mining programme to some extent, par
ticularly near the end of the programme. On the \Yider
benches sufficient material could be left outs ide the 300
ft. l i mit to accommodate the shovel during these periods.
Jlowever when the benches became narrower, th is flexibili.ty
was lost.
It was obvious to us after the mining prog r amme
was completed, that the mining sequences as r ecommended by
Colder Brawner were not only jus t ified but well thought
out. Although it delayed the mining programme to some
ex tent, we feel that it wa s a major fac tor contributing to
the successful completion o{ the programme.
RESTRI CTION ON NIGHTTIME OPERATION
The restriction of daylight operation only was
ini tiated originally because the visual monitoring could
not be carried out at night time. It was recognized, how-
MONITORING OF THE HOGARTH PIT HIGHWALL 133
ever, that we were dealing 1\'ith a moving mass and that
failure 1vould occur lvith time. 1 t \vas the opinion of all
the consulting people that we should complete the mining
as quickly as possible so that we would be out of the area
in the shortest possible time. The daylight hours only
restriction would result in lengthening the time involved
in completing the program and also result in many lost
equipment hours and an overall inefficient mining opera
tion. Steep Rock personnel installed a system of metal
hilite lamps to illuminate the wall so that mining could
be carried out on a twenty-four hour basis. Six 1500
watt lamps were used and were positioned such that the
entire wall would be illuminated. Golder personnel in
spected the area after installation and agreed that the
lighting was adequate to monitor the wall visually and to
operate on a twenty-four hour basis.
The plan was explained to a delegation from the
union who visited the wall at night to inspect the lighting .
They decided to take the request back to the members, and
the majority of the membership voted not to work in the
area at night time. As a result, mining inside the Green
Line (300 foot limit) was carried out during day-light
hours only to the end of the program.
Of all the restrictions imposed, this decision had
the greatest economical impact. As estimate of 600,000
cubic yards of net excavation was lost throughout the
134 C, BRAWNER, P, STACEY AND R, STARK
operation hecause of the ineffitient use of equipment
result ing from the restricted operation in the Zone . It
was necessary to use the largest shovel on the property i.n
the No. 1 Zone because of its dependability and its ele
vated cab. Consequently, tho shovel cou ld not be used
elsewhere and was i dle during nightti me , i.e. for lS hours
per day . In terms o f direct cost dollar s , it i s dif ficul t
to put a value on it. Indirec t cos ts result ing from the
600,000 cubic yards shortfall, would be s ignificantly
higher than the direct costs, when the long term ore supp ly
outlook is considered.
UNI ON INVOLVEMENT
Steep Rock lron Mi nes Limited have established a
policy over the years of keepin g all emp loyees info rmed
cont inually of any changes or decis ions which affect them
directly or indi rect ly. This information is presented to
them on the job by supervisors, by technica l people , and
through their un ion.
Because of the se riousness of the situation, an
even greater emphasis was placed on fol l01,ring th is policy
in al l aspec t s of the No . 1 Zone prob lem. When t he wall
movement ini tially acce lerated i n August 1974, and mining
in the area '"as temporarily suspended, the union represen
tatives were notified and the situation was expla ined to
them.
MONITORING OF THE HOGARTH PIT HIGHWALL 135
Golder Associates completed their evaluation and
the monitoring system \HIS installed. When the reconnnen
dations ~~ere all met, the union executive attended a
briefing session with the company and Golder's represen
tatives. Subsequently, all open pit employees on each
shift were briefed on the monitoring and mining system.
One union member was selected daily as a guard to visually
inspect the wall. At the request of the union, a second
guard was added to each shift to reduce the monotony and to
improve the visual inspection by allowing the guards to
spell each other off after various time periods.
To further inform the employees, the monitor
results were posted daily on the bulletin board in the mine
dry area. Comments were also added to explain any abnormal
movement recorded. The top of the wall was also inspected
dai.ly by the scalers and their comments were posted on a
blackboard in the dry area.
Considering all aspects of the No. 1 Zone problem
and subsequent solutions, we are convinced that the policy
of keeping all employees informed is well worthwhile. We
feel that our emphasis on communications has paid off with
better employee relations, better union-management rela
tions, and a greater desire on the part of most employees
to complete the job successfully.
136 C. BRAW~ER, P, STACEY AND R, STARK
CHOlCE Of PERSOl\NEL AS WALl. GUARDS
The decision to use hour l y r at ed employees us
guards on the wall had an interes ting psychologica l e ffect
on thos e working in the area .
As mentioned previous ly, two guards were se lected
from each shift. However, t ho guard duties were ro tated so
that most employee s working in the area t ook their t u r n.
Only one gua rd \vas changed eac.:h day so t ha t at least one
of the gua r ds had experience at all times . The guards
were se l e cted at the discretion of the ope r ating fore men.
There were throe advantages in using hour l y rated
personnel and rotating t hem. First of all, monotony was
not a p roblem because or the r otation. Secondly , we
created a si tua t i on where hourly employees were taking
respons i bi l i ty , t o s ome extent, for the sa fe t y of their
fellow workers. Thirdly, most emp l oyees had the oppor
t unity to experience t he diff iculties and r esponsi b i lities
of those guarding. This ga ve each of them a better appreci
ation of what was going on .
Steep Rock Management was concerned about fac t ors
wh i ch could a U ect t he efficiency of t he gu a r ds. Most of
t he guarding was required i n wi n ter wea ther , and there was
a tendency to keep t he window c losed, ther eby elimina ti ng
sound a s a monitoring tool . A light was requ ired i n the
s hack , but it had a tende ncy to cut down on t he effective
ness of visual monitoring . I t also allowed the gua rds to
MONITORING OF THE HOGARTH PIT HIGHWALL 137
read, which had an adverse affect because their eyes had to
adjust to the distance change. The installation in the
guard shack of the seismograph recorder had both positive
and negative effects on the guarus . The fact that it was
located there, gave the men more confidence that any indi
cation of movement would be noticed immediately. However,
there was a tendency for the guards to watch the recorder
rather than the wall, thus reducing the visual monitoring.
The seismograph was not meant to replace, in any 1,.ray, the
visual monitoring system.
ACKNOLI'fEDGEMENTS
The authors wish to thank the Management of Steep
Rock Iron Mines Ltd., both for their support and readiness
to assist throughout the program, and for their permission
to publish this paper.
The advice and assistance of many members of the
Golder organization is also acknowledged. In particular
the perseverance of the engineers who acted as field men
is gratefully appreciated.
Finally, thanks are due to many members of the
Steep Rock staff for their cooperation and assistance
throughout the programme.
138 C, BRAWNER) P, STACEY AND R, STARK
REfERENCES
1. BRAWNER, C.O., (1968) "The Three Major Problems in Rock Slope Stability in Canada". Second International Conference on Surface Mining, Minneapol1s .
2 . BRAWNER, C.O. & GILCHRIST, H. G. (1970) "Case Studies of Rock Slope Stability on .Mining Projects" . Eighth Annual S•m1os ium on En•inoer in Geolo • and Sol! Eng ineering, Pocatello, I a1o.
3 . BRAWNER, C.O. (1970) "Stability Invest igations of Rock Slopes in Canadian Mining Projects" . Second International Rock Mechanics Conference, Belgrade , Yugos lav1a .
4 . BRAWNER, C.O. (1971) "Case Studies of Stability on Mining Projects". Stability in Open Pit Mining A.I.M.E., New York .
s. BRAWNER, C.O . (1974) "Rock Mechanics in Open Pit Mining". Supplementary Report, Theme Three - Surface 1\forkings, Proc . 3r d Int . Conf. on Rock ~lcchanics , Denver.
6 . KENNEDY, B.A. (1971) "Methods of Monitoring Open Pit Slopes''. Proceedings, Thirteenth Symposium on Rock Mechanics, Urbana, Illinois .
WRITTEN DISCUSSION OF TbCHNICAL PAPbRS
DISCUSSION Of: "Monitoring of the Hogarth Pi t Highwall, Steep Rock Mine, Atikokan, Ontario" by
139
C. 0. Bra~vncr, P. F. Stacey and R. Stark. Presented at the lOth Canadian Rock Mechunics Symposium, Kingston, Ontario, Septemher 1975.
SUBMITTED BY: P. N. Calder, Associate Professor, Depart ment of Mining Engineering, Queen's University, Kingston, Ontario, K7L 3N6.
In thi."> paper, the authors state, "Durjng the night
shift when no equipment was operating in the zone, occa-
sional small movement signatures appeared on the seis-
mograph trace. In the daytime however, se i smic indications
of this typo were masked by mine equipment signatures so
that warning was not available from the seismic instrumen-
tation. This confirms the experience of Kennedy (1972) on
the practical limitations of the seismic monitoring tech -
nique."
I was involved in the monitoring of the Hogarth
Pit Highwall, having been engaged for this purpose by the
Ontario Ministry of Natural Resources. It was upon my
recommendation that the seismograph unit was employed as a
monitoring instrument, however, 1 was not jnvolved in the
operation of the seismograph or the interpretation of the
data.
My main purpose in recommending the seismograph was
to provide a continuous sensitive warning system. The sur-
140 WRITTEN DISCUSSION
f ac e cxtens ometers woul d only trigger t he warning system
fo l lowi ng a tot al pr e -set movement. In my opinion, i f an
amount of movemen t less t han th e magni t ude requi red t o
t rigger the warn i ng system occured sudden l y , the mass coul d
f ai l. For examp le , if within a fi ftee n minute period t he
mass moved 1/4 of an inch , thi s would be very significant,
but would not neces sari ly trigger the sys tem.
Regarding the masking of the seismic noise generated
by th e movin g mass, i n the pa per re f erred to (Refe rence 6)
by Kennedy, he states, "Wi th experience, it i s possible to
rec ognize wi t h ease the cu l t ura l no i se gener ated in the p it
by drill s , trucks, shovels , locomotives , etc. Earthqua kes
a rc also eas ily i den tifiable with a ve r y defi nite wave f or m
envelope. The r oc k noi ses emana ting from an uns table zone
arc identif i able by their character i stic envelope shape, a
f requency us uall y between six and nine He rtz, and a c harac
t eristi c irregular amplitude."
I a lso felt that t he seismograph would provide s uf
f icient confidence in the abili ty to kn ow the s tate of
movement t o permit n i ght operat i ons , and s t il l feel t his
shoulu have been possible . My feedback on the usc of t he
seismograph in th is i nstan ce was tha t it was a pTact i cal
method of provid ing con tinuous monitor ing and wa s accep ted
by the people involve d on si t e as such.
WRI TTEN DISCUSS ION 141
DISCUSSION OF: "Rock Perrorma nce Considerations for Shallow Tunnels in Bedded Shales with High Lateral Stresses" by J. D. Morton, K. Y. Lo and D. J. Be l s haw . Presented a t the lOth Canadian Rock Mechan i cs Symposium, Kings t on, Onta rio, September 1975. ·
SURMITTED BY : J. H. 1. Palmer , Geotechnical Section, Division of Building Res ea rc h, National Research Counci l of Canada, Ot tawa, Ontario, KIA OR6
The a ut hor s have pr esented many aspects of a com
plex prob lem. This discussion concerns one fac et only, t he
measured hor izontal stresses .
Reference has been made to in si tu stre ss meas ure-
ments performed by t he wri t e r at Thor old , Ontario . Unfor
tunately , one of t he results cited in the text i s mis quoted
and the error is rather significant. At Thoro ld, the ma j or
principal st resse s varied from 1200 to 2100 ps i (8.3 to
14. 5 MPa ) and the minor principal s tresses var i e d fr om 760
to 1750 psi (5.2 to 12 .1 MPa) . The r e were no t ens ile
s tresses. The 200 psi tension a ttributed to the Thorold
t ests was, in fact, measured i n the Collingwood formation.
Eve ry test i n two different membe rs of t he Lock port fo r
mation and in the upper member of the Cl inton group a t
lborold i nd icated very high horizontal stress, on the
average about 1400 psi (9.6 MPa ) compress ion (i.e. about 20
t imes the overburden stress) .
The Dundas and Collingwood s hales are l ayered
depos i t s cha r acte r i zed by distinctly d ifferent physical
142 WRITTEN DI SC USSION
properties in some of the layers. Overcoring tests in
such deposits generally have indicated high stresses in
the "soft" layers and low (or tensile) stresses in the
"hard" layers. The ZOO psi t ension was attributed to a
particularly competent portion of the Collingwood for
mation. The writer agrees with the authors that it is
difficult to explain completely the abrupt stress changes
from 1000 psi compression to 200 psi tension, but there is
no reason to doubt the test results. The magnitude of the
tensile stresses might be questioned, since that is a
matter of interpretation of the measured deformations and
in situ deformation modulus; there is no doubt that the
tests indicateu high compressive stresses and tensile or
essentially zero stresses in close proximity.
More data similar to those presented by the authors
are required to permit full assessment of the extent and
engineering significance of this phenomenon of high in-situ
horizontal stress. The writer strongly urges anyone who
has the opportunity to support more detailed geotechnical
investigations of future tunnelling projects to include in
contract specifications carefully planned monitoring pro
cedures, and to publish the data.
LIST OF DELEGATES ATTENDING
THE TENTH CANADIAN ROCK MECHANICS SYMPOSIUM
ARF.KION, Herve Civil Engineer Racey MacCallum & Bluteau Limited 8205 Montreal - Toronto Blvd. Montreal, Quebec
BASSERMAN, Robert R, Mining I:ngineer 541 College Street Kingston, Ontario
BAUER, Dr. A. Head, Mining Engineering Department Queen's Univers ity, Goodwin Hall Kingston, Ontario
BAWDEN, William Graduate Student, Ci vil Engineering Department University of Toronto Toronto, Ontario
BEAVIS, Albert Drilling & Blasting General Fo reman Anaconda Company P.O. Box 689 Butte, Montana U.S.A. 59701
BELSHAW, D. J. Morton, Dodds & Partners 1263 Bay Street Toronto, Ontario
BLACKWELL, G. H. Mining Engineer Brenda Mines (Noranda Group) P.O. Box 420 Peachland, B.c:
BLAGDON, S. A. Field Geologist Advocate Mines Limited Baie Verte, Newfoundland
143
144 LI ST OF DELEGATES
BLAGONA, N. President & Managing Director Geotechnical Associates Limited 109 Water Street, P.O. Box 5893 St. John's, Newfoundland AlC 5X4
BOYER, Luc P.ngineering Geologist 537 Curzon Street St. Lambert, Quebec J4P 2V9
BRAWNER, C. 0. Principal Golder, Brawner & Associates 224W. 8th Avenue Vancouver, B.C.
BRAY, Richard C. E. Consulting Engineer 21 Sydenham Street Kingston, Ontario
BROOKER, Elmer W. President EBA Engineering Consultants Limited 14535 - 118 Avenue Edmonton, Alberta TSL 2M7
BULLOCK, Gerald T. Assistant to Manager, Outside Mines Cominco Limited Trail, B.C .
CALDER, Dr. P. N. Associate Professor, Mining Enginee ring Department Queen's University, Goodwin Hall Kingston, Ontario
CANT, S. A. Senior Materials Engineer Ontario Ministry of Transportation & Communication 1201 Wilson Avenue Downsview 464, Ontario
CAPELLE, J. F. Vice President Roctest Limited 665 Pine Street St. Lambert, Quebec
LIST OF DELEGATES
CARMICIIAEL, Thomas J. Geotechnical Engineer Ontario Hydro Research R272A, 800 Kipling Avenue Toronto, Ontario
CATCHPOLE, George Jena Instrnments Ltd. 199 Ashtonbee Roau Scarborough, Ontario
CHUNG, Stephen Research Physicist Canadian Industries Limited Explosives Research Laboratory McMasterville, Quebec J3G 1T9
CLARK, Paul Assistant to the Mine Superintendent Cassiar Asbestos Corporation Limited Cassiar, B.C. VOC lEO
COATF.S, Dr. D. F. Director General Canmet Department of Energy, Mines & Resources SSS Booth Street Ottawa, Ontario KIA OGl
CONNOLLY, Brian H. Assistant Mines Planning/Layout Engineer International Nickel Company of Canada Pipe Mine Thompson, Manitoba
CROSBY, William A. Graduate Student, Mining Engineering Department Queen's University 642 Aylmer Crescent Kingston, Ontario K7M 6Hl
DANNENBERG, Joseph Publisher ABA Publishing Company 406 W. 3Znd Street Wilmington, De. U.S.A. 19802
145
146
DJ\S, Dr. Buddheswar Assistant Profess or
LIST OF DELEGATES
Department of Mining & Engineering Laval University Quebec 10, Quebec GlK 7P4
DEREN IWSKI, T. M. Assistant Planning Layout Engineer International Nickel Company Limited Birchtree Mine Engineering Thompson, Mani to ba R8N 1P3
DEVENNY, Daviu Senior Geotechnica l Engineer, Project Manager/Principal EBA Engineering Consul tant s Limited 14535 - 118 Avenue Edmonton, Alberta TSL ZM7
DODDS, Robert B. Partner Morton, Dodds & Partners 1263 Bay Str eet Toronto, Ontario MSR ZCl
DUBE, Pierre Student Mineral Engineering Department A-374 Ecole Polytechnique Montreal, Quebec
DUNCAN, Derryl Civil Engineer She ll Canada Llmiteu 1027 8th Avenue , SW. Calgary, Alberta
DURAND, Marc Professor of Geol ogy Universite de Quebec C. P. 8888 Montr6al, P . Q. H3C 3P8
DUSSEAULT, Maurice B. Doctoral Stuuent , Department of Civil Eng ineer ing University o f Alberta Edmonton, Alberta
FAUCHER, Pierre Engineering Geologist
LIST OF DELEGATES
Lalonde, Girouard, Letendre & Associates 800~Est-de Maisonneuve Montreal, Quebec H2L 4L8
FRANKLIN, Dr. J. A. Franklin Trow Weir-Jones Limited 43 Baywood Road Rexdale, Ontario M9V 3Y8
GALBRAITH, John Graduate Student, Mining Engineering Department Queen's University 11 Clergy Street \'/., Apt. 3 Kingston, Ontario
GALE, John E. Research Scientist Geological Survey of Canada 601 Booth Street Ottawa, Ontario KIA OE8
GARG, 0. P. Supervising Engineer Iron Ore Company of Canada P.O. Box 2155 Schefferville, Quebec GOG 2TO
GARTSHORE, R. W. Asbestos Fibre Division Canadian Johns-Manville Asbestos, Quebec
GILL, Denis E. Professor Ecole Polytechnique de Montreal C.P. 6079-St. A. Montreal, Quebec H3C 3A7
GORMAN, Alastair Senior Engineer Franklin Trow Weir-Jones Limited 43 Bay\vood Road Rexdale, Ontario M9V 3Y8
C:OULET, Norman Structural 6eologtst Queen's University Miller Hall Kingston, Ontario
147
148 LI ST OF DELEGATES
HANDA, S. C. Graduate Student, Civil Engineering Department Queen's University Kingston, Ontario
HARKER, Richard Jones & Laughlin Benson Mine Star Lake, New York U. S.A.
HARRISON, David M.T. S. Systems 342 Millard Avenue Newmarket, Ontario L3Y 1Z4
HARTMAN, Gerhardt P. Head, Regulated Surface Operations Branch Alberta Depa rtment of Environment 10040-104th Street Edmonton, Alberta
HEATER , Raymond D. Technician, Mining Engineering Department Queen's University, Goodwin Hall Kingston, Ontario K7L 3N6
HEDLilY, D. G. F. Research Scientist Canmet P.O. Bo:x: 100 El liot Lake, Ontario PSA 2J6
HILLIER, D. R. Engineer, Mining Engineering Department Queen 's University, Goodwin Hall Kingston, Ontario K7L 3N6
HOFFMAN, W. A. Chief-Mines Division Ministry of Natural Resources, Ontario Government Room 1312, Whitney Block Queen's Park Toronto, Ontario
HOGG, Alan Ontario Hydro Toronto, Ontario
HOLMES, George F. Geologist
LIST OF DELEGATES
Sherritt Gordon Mines Limited P.O. Box 198 Leaf Rapids, Manitoba ROB lWO
ISAAC, E. W. Regional Mines Engineer Ministry of Natural Resources , Ontario 1112 Kings\Y"ay Sudbury, Ontario P3B ZES
JEREMIC, Dr. M. Associate Professor of Mining Department of Mineral Engineering University of Alberta Edmonton, Alberta TSL ZM7
JOB, Arthur Leslie Mining Engineer Can met 555 Booth Street Ottawa, Ontario
JOIINSON, Stephen M. Junior Mining Engineer Caland Ore Company Limited Atikokan, Ontario
KALlA, Tej endra Geotechnical Engineer Iron Ore Company of Canada P.O. Box 2155 Schefferville, Quebec GOG ZTO
KHAN, Farrukh Terra-Scan Limited Toronto, Ontario
KING, Dr. M. S. Professor Department of Geological Science University of Saskatchewan Saskatoon, Saskatchewan S7N OWO
KINGSTON, Dr. Paul W. Industrial Minerals Geologist New Brunswick Department of Natural Resources Centennial Bldg. Fredericton, N.B.
149
150 LIST OF DELEGATES
KURPURST, Pavel Geological Survey of Canada 601 Booth Street Ottawa, Ontario KlA OE8
LACASSE, Maurice Development Engineer Bell Asbestos Mines Limited P.O. Box 99 Thetford Mines, Quebec
LADANYI, Dr. B. Professor Deale Polytechnique C.P. 6079, Station A Montreal, Quebec H3C 3A7
LAFRANCE, Claude Student, Mineral Engineering Department Ecole Polytcchnique 2500 Marie Guyard Montreal, Quebec
LAVALLEE, Jean - Francais Canadian J ohns -Manville Asbestos, Quebec
LECOMTE, Paul Chief of Division, Special Studies Geological Services Hydro Quebec 855 Stc. Catherine, F.st Montreal, Quebec HZL 4M4
LECUYER, Norman Student, Mining Engineering Department Queen's University, Goodwin Hall Kingston, Ontario K7L 3N6
LEE, llyun -Ha Consulting Engineer Harrison Bradford & Associates Limited 71 King Street St. Catharines, Ontario LZR 3H7
LYLE, Glenn Graduate Stud~nt, Mining Engineering Department Queen's University, Goodwin Hall Kingston, Ontario K7L 3N6
LIST OF DELEGATES
MACKINTOSH, A. David Rock Mechanics Technician Potash Division Com in co Limited Vanscoy, Saskatchewan SOL 3JO
MACRAE, Allan Rock Mechanics Engineer 184 Ordnance Street Kingston, Ontario
MADSEN, James D. R.M. Hardy & Associates Limited 4810 93rd Street Edmonton, Alberta TSJ 214
MARCH, R. R. Chief Inspector of Mines Department of Mines & Energy Imperial Oil Building 85 Elizabeth Avenue St. John's, Newfoundland
MARCIL, Denis President Roctest Limited 665 Pine Street St. Lambert, Quebec
MATEER, J. D. Master Haileybury School of Mines Haileybury, Ontario POJ lKO
MATHEWS, K. E. Professor Department of Mineral Engineering University of British Columbia Vancouver 8, B.C.
MATSON, James Canadian Industries Limited 630 Dorchester W. P.O. Box 10 Montreal, Quebec H3C 2R3
151
152 LIST OF DELEGATES
MCCRODAN, P. B. Director, Mines Engineering Branch Ontario Government - Ministry of Natural Resources Room 1309, \'/hi tney Block, Parliament Buildings Toronto, Ontario M7A 1W3
MCGUIGAN, Hugh Survey Representative Norman Wade Co. Ltd. 75 Milner Avenue Scarborough, Ontario
MCKINLEY, Donald Mississauga, Ontario
MCLENNAN, John Graduate Student, Department of Civil Engineering University of Toronto Toronto, Ontario
MCLEOD, Peter C. General Mine Superintendent Noranda Mines Limited, Geco Division P.O. Box 100 Manitouwadge, Ontario POT ZCO
MEECH, J. A. Special Lecturer, Mining Engineering Department Queen's University, Good\~in Hall Kingston, Ontario K7L 3N6
MICHAUD, Robert L. Student, Mining Engineering Department Queen's University 1236-401 Princess Street Kingston, Ontario
MIERZWA, \'Hadyslaw Post Doctor Fellow, Mining Engineering Department Queen's University, Goodwin Hall Kingston, Ontario K7L 3N6
MIHAILOFF, Nick Thor Instrument Company Limited 101 - 1644 W. Broadway Vancouver, B.C. V6J 1X6
MONDOLONI, Guy Rousseau Sauve & 1860 edifice Sun Montreal, Quebec
MORRIS, Peter G. Professor
LIST OF DELEGATES
Warren Life
H3B 2V6
University of Waterloo 178 Sunview Street Water loo, Ontario NZ L 3Vl
MORTON, John D. Partner Morton, Dodds & Partners 1263 Bay Street Toronto, Ontario MSR ZCl
NANTEL, J acques Assistant Professor, Mining Engineering Department Queen's University, Goodwin Hall Kingston, Ontario K7L 3N6
NAUER, Walter Assistant General Manager Kern Instruments 163 Echo Drive Ottawa, Ontario KlS 1M9
NOTLEY, Keith R. Graduate Student, Mining Engineering Department Queen 's University, Goodwin Hall Kingston , Ontario K7L 3N6
O' HARA, Brian York University Toronto, Ontario
OLIVER, Keith Mine Superintendent Adams Mine Kirkland Lake, Ontario
OLIVER, P. H. Supervisor of Rock Mechanics I nco Mines Engineering Copper Cliff, Ontario POM 1NO
153
154 LI ST OF DELEGATES
PAKALNIS, V. Mine Research Engineer - Rock Mechanics Falconbridge Nickel Mines Limited Falconbridge, Ontario
PALMER, Dr. J. H. L. Research Officer Geotechnical Section Division of Building Research National Research Counci l Ottawa, Ontario
PITEAU, Douglas Director Piteau Gadsby MacLeod Limited 1409 Bewicke Avenue No1·th Vancouver, B. C . V7M 3C7
POTTS, W. H. Superintendent of Mines Research Saskatchewan Government (Department of Mineral Resources) 1914 Hamilton Street P.O. Box 5114 Re gina, Saskatchewan S4P 3PS
PRESTON, Chris J. Engineer, Mining Engineering Department Queen's University, Goodwin Hall King ston, Ontario K7L 3N6
PRICE, Dr. R. Head, Department of Geological Sciences Queen's University Kingston, Ontario
RIDDELL, Captain D· v. B. Mas t e1· ' s Student Royal Military College Kingston, Ontario
ROEGIERS, Dr. Jean-Claude Dep~rtment of Civil Engineering University of Toron to Toronto, Ontario MSS lA4
ROWAN, Ronald Sales Representative Jena Ins truments 199 Ashtonbee Road Scarborough, Ontario MlL 2Pl
LI ST OF DELEGATE S
SAURIOL, Gilbert Underground Mines Superintendent Gaspe Copper Mine s Limited Murdochville, Quebec
SCHWELI.NUS, Dr. J. E. G. President-Consulting Mining Engineer J. Schwellnus & Associates 1153 de Bougainville Street St. Bruno, Quebec J3V 3E8
SHAW, Rooney c/o Shawinigan Engineering Company 620 Dorchester Blvd. W. Montreal , Quebec
SIIILLABF.F.R, John H. Project Manager Dames & Moore Consulting Engineers Suite 1300, 55 Queen Street East Toronto, Ontario MSC 1R6
SIMON, Robert Jones & Laughlin Benson Mine Star Lake, New York U.S.A.
SMITH, John D. President John D. Smith Engineering Associates Limited 155 Falkirk Terrace Kingston, Ontario
SMITH, Kerry Student, Mining Engineering Department Queen's University, Goodwin IJall Kingston, Onta r io K7L 3N6
SOE, Maung Maung Graduate Student University of Toronto Toronto 5, Ontario MSS 1A4
STACEY, P. Senior Engineer Golder Brawner & Associates 224 - W 8th Avenue Vancouver, B.C.
155
156 LIST OF DELEGATES
STARK, Robert 0. Senior Mining Engineer Steep Rock Iron Mines Limited Atikokan, Ontario POT lCO
SUCHAR, A. J. Mine Engineer Allan Potash l\1ine Operators Limited Allan, Saskatchewan SOK OCO
TAPICS, John Engineer, Coal Department Energy Resources Conservation Board 603 6th Avenue, S.W. Calgary, Alberta T2P OT4
TAYLOR, Howard Jones & Laughlin Benson Mine Star Lake, New York U.S.A.
THEIS, Nicholas J. Student, Department of Geological Sciences Queen's University Kingston, Ontario
THOMPSON, J. C. Professor, Civil Engineering Department University of Waterloo Waterloo, Ontario N2L 3Gl
VAN RYSWYK, Roy J. Engineering Geologist H.Q. Golder & Associates Limited 3151 Wharton Way Mississauga, Ontario L4X 2B6
VONGPAISAL, Somchet Operational Research Engineer Falconbridge Nickel Mines Limited Falconbridge, Ontario
WAGNER, H. Assistant Director Chamber of Mines of South Africa P.O. Box 809 Johannesburg, South Africa
LIST OF DELEGATES
I~ALT0.:-.1, Terry R. Technical Sales Engineer Canada Cement Lafarge Limited 240 Duncan MlJl Road Don ;...{jUs, Ontari.o 1-BB 3H4
WILKES, Leroy E. Pit Operations Superintendent Anaconda Company P.O. Box 689 Butte, Montana U.S.A. 59701
WILSON, E. B. Associate Professor, Mining Engineering Department Queen's University, Goodwin Hall Kingston, Ontario K7L 3N6
1\'IN, U. University of Alberta Edmonton, Alherta
ZEllNER, Dieter Manager, Photogrammetry Division Wild Leitz Canada Limited 881 Lady Ellen Place Ottawa, Ontario KlY 4Gl
157
158
LIST Or COMPAN I ES SUPPORT I NG
THI: TENTH CJ\1-11\DIAN ROCK MJ::CHAN TCS SYMPOSIUM
Jena Instruments Ltd. 199 Ashtonbee Road Scarborough, Ontario
Sympos ium Representatives: Mr. George Catchpole , .Mr. Ron a ld Ro1~an
Telephone: (416)751 -3648 , (604)584-0206
Kern Instruments of Canada Ltd. 163 Echo Drive Ottawa, Ontario KlS 1N9 Sympos ium Representative: Mr . Walter Nauer Telephone: (613)235 - 4908
M.T.S. Systems 342 Millard Avenue Newmarket, Ontario L3Y 1Z4
Symposium Representat ive: Mr. David Harrison Telephone: (416)895-7000
Roctest Ltd. 665 Pine Street St. Lambert, Quebec
Sympos ium Representative s : Mr. Denis Marcil, Mr. J. F. Capelle
Telephone : (514)465-1113
Structural Behaviour Engineering ~ahoratories Inc . P.O . Box 9847 Phoenix, Arizona 85068
Representative: Mr. John D. Hess Telephone: (602)272 -0274
Thor fn strwnent Co. Ltd . 1644 West Broadway Vancouver, B.C.
Symposium Representative: Mr. Nick Mihailof£ Telephone: (604)732 -0525
Wilcl-Leitz Canada Ltd. 881 Lady Ellen Place P.O. Box 3520, Station " C" Ottawa, Ontario KlY 4Gl Symposium Representative : Mr . Deiter Zeuner Telephone: (613)722 - 4231
159
ADDENDA
CORRECTIONS TO VOLUNE 1 OF SYt1POSIUM PROCEEDINGS
160 ADDENDA
1. Substitute the figures below for the figures on pages 173 and 175 respectively . tpo
300
Sel llemenl
due to 200 Consolidot1on
(feel)
0 0
40
20
100 200 300 400 500 Depth of '"'''ol Sediment· ((eel}
PercetH
Reduclion
in Loyer
Thicl~>ess
FIGURE 3 PREDICTED SETTLEMENT DUE TO CONSOLIDATION OF TAILINGS FINES
100
80 -
~
.!?
-~ 60 0 c 0 u
c 4 0 .. ~ ..
a.
20
Length of Droiooge Path (feet)
I 2 3 6 10 20 50
I
0 '----0~.,------' 10
Tim e in Years 100 1000
FIGURE 4 TIME RATE OF CONSOLIDATION FOR VARIOUS LENGTHS OF DRAINAGE PATH
ADDENDA
2 . Line 19 on page 418 delete the word 'strength'.
3. End of sentence line 7, page 420, add '(Morgenstern and Dusseau 1 t , 1 9 7 S) ' .
4 . Last line page 424 add '(Bjerrum 1961)' .
5 . Line 6, page 246 change 'figure 13' to 'figure 2'.
161
6 . Line 12, paragraph 2, page 438 delete word 'result'.
7 . Add the following set of references below. Note that these references are to replace those presently tabulated on pages 445-446.
RF.flERENCES
1. Allen, A. R., Sanford, E. R.; 1973; "The Great Canadian Oil Sands Operation"; in, Guide to the Athahasca Oil Sands Area, Information Series 65; Published by the Alberta Research Council, Edmonton, Alberta; pp 103 - 122.
2 . Bjerrum, L. (1961); "The Shear Strength of a Fine Sand''; Norwegian Geotechnical Institute Publication No. 45.
3 . Brooker, E.\'1., freland, 11.0. (1964); "Earth Pressure at Rest and Stress History"; Canadian Geotechnical Journal, Vol. 11, No. 1, 1965.
4 . Carrigy, M.A. (1973); "Introduction and General Geology"; in, Guide to the Athabasca Oil Sands Area, Information Series 65; Published by the Alberta Research Counci 1, Edmonton, Alberta; pp 1 - 14.
S. Carrigy, M.A. (1973); "Mesozoic Geology of the Fort McMurray ·\r~a"; in, Cuid~ to the Athahasca Oi I Sands Area, Information Series 65; Published by the Alberta Research Council; Edmonton, Alberta; pp 77 - 102.
6 . Carrigy, M.A. (1972); Personal Communication regarding the amount and duration of pre-existing sediment load.
7 . Casagrande, A. (1973); Personal Communication regarding the origin and strength in dense sands subjected to geological aging.
162 ADDENDA
8. Dusseault and Morgenstern (1975); Personal communication regarding the origin and strength in oil sand deposits and of natural slope measurements.
9. Hardy, R.N. ( 19 7 4) ; !-ler son a 1 communi cation regan! ing failures in oll sand slopes.
10. Hurdy, R.M., Hemstock, R.A. (1963); "Shear Strength Characteristics of the Athabasca Oil Sands "; K.A. Clark Volume, Tnformation Series No. 45; Published by the Alberta Research Council, Edmonton, Alberta, pp 109 - 122.
11. Hoek, E., Lorde, P. (1974); "Surface Workings in Rocks"; Proceedings of Third Congress of the International Society for Rock Mechanics Denver, Co l orado, September, 1974.
12. Hoek, r::., Bray, J.W. (1974); "Rock Slope Engineering"; Institute of Mining and Metallurgy, London.
13. Mol lard, J. (1962); Persona l communication regard ing measurements of natural slopes in the Athabasca Oil Sands Area.
14. Patton, f.D., Deere, n.V. (1970); "SignHicant Geological factors in Rock Slope Stability", Planning Open Pit Mines; South African Institute of Mining and Metallurgy, Johannesburg, September 1970.
15. Peck, R.B., (1962); "Art and Science in Subsurface Engineering"; Geotechnique , 1>1arch.
16. Sinc lair, S., Brooker, E. l'l. (1967); Procoodings of the Geotechnical Conference, Oslo.
17. Terzaghi, K. (1936); "Presidential Address to the First International Conference on Soil Mechanics and founuution Engineering, Harvard University.